Is it easy to learn to mouse with your other hand? Or you got experience with an ergonomical mouse?

Yes, unless you have those one-side ergonomic mouses. Just swap RMK and LMK, makes it easier to switch. It took me 3-4 days tho to get used to it, but not the to level of FPS games ofc.

Haven't tried this but I tried to learn to write with my left hand. It's not that hard, just requires some training. And I believe learning mouse is easier because it's mirrored.

Also, this reminds me this video. Though using mouse is not motor learning so expect it to be a lot sooner than 8 months. :)

Ooh, if you have a repetitive strain injury you need to watch that. It will happen even faster to your other wrist since it won't be as strong as the one you use all the time. Get a wrist support strap to support the weaker wrist that you're learning to mouse on, and rest the injured one.

Might be wise to use a wrist support in the future as a RSI has a tendency to come back once it happens one time. Give your wrist time to recover. Don't put a wrist strap on and continue the behaviour just because it doesn't hurt with it on. That will make it worse in the long run. Give it a rest, then start wearing a wrist strap going forward to prevent further injury.

I have some experience with RSI that I got from a job I worked in years ago. I'm fine now, but if I am going to be typing a lot, I strap up my wrist.

Only took me a couple of hours to be browsing and doing easy stuff without thinking too much about it, same with writing. Typing took a bit longer but that was more to do with my arm defaulting to a WASD position I think. Anything where you're not doing complicated stuff with the rest of your arm you'll get the hang of quite quickly.

Learning how to throw a ball though? Utterly impossible :)

You get used to the change quickly as far as pointing and clicking goes. However, mouse+keyboard coordination is a different story. Games that use WASD and pals or 1-5 and F1-F5 keys will be a problem. These keys are on the left side of the keyboard and so, it's difficult to use your right hand with these. I imagine you can, but everything will be mirrored. You'd need custom key mapping to the right side if the game supports it. I'm right-handed but I started using the mouse with my left hand to relieve the pain from the RSI in my right hand. I don't play as much as I did in the past, but when I play games like these, I just switch to my right hand for the duration of the playing session.

My right hand had surgery on it last month, I switched to using my left hand for the mouse and other than Day One oddities, and experimenting with making right click left, and left click right (I ended up going back to left is left click, right is right click), it feels pretty natural to me. I can play games and do pretty much everything with the computer left handed now. Although my typing speed dropped drastically.

It makes it feel like someone else is holding your....mouse ;)

You can train (and memorize) basics within few days, but even months is not enough to master other hand to level that you can do something responsible like work or playing fps. Has similar problem few months ago, and i even working in photoshop a little after month of immobilizing right hand, but it is so clunky and unusual. But it is okay for basics - surfing internet, reading, editing, even using gamepad in games, completed mass effect 1-3 with wrist support :) So if you want to reduce stress on the arm - do in in usual but regular doings.

It depends on your brainactivity tbh.
https://www.psychologytoday.com/us/blog/the-asymmetric-brain/201909/the-left-handed-brain

To force yourself to use your left hand even if your right hand could do all the work without problems can even lead to headaches.

Unless you're talking about playing a fast-paced FPS game, I don't see any difference using a mice with either hand. But perhaps that's because I'm used to switching between holding a graphics tablet pen with one hand while using a mouse with the other hand.

I started using mouse as a kid while being left handed, and I used it in only way it was available - on the right side, just like everybody else. I recently (2-3 years ago) tried using mouse with my left hand, and while not as precise as with right hand, learning how to do it is certainly doable. Just like Resebonbon said above, don't count on being master shooter in FPS games.

I did this several times while at work.
but haven't tried with gaming.

shouldn't be too bad to just switch if all you're doing is browsing the web. gaming is something different though, especially if you need to be quick and snappy. i don't know much about ergonomics, if you saw my setup, you'd probably laugh.. i doubt anyone uses their pc the same way as i do. buuut, maybe check out something like a vertical mouse? probably not that exact one, it was just the first thing that showed up when i googled it. i'm sure logitech makes a decent one.

I usually have some carpal tunnel pains and I change the mouse to the other hand. At the beginning it is weird, afterwards it is ok. Scrolling, clicking and most of the basic staff is easy. As others said, no heavy duty gaming and you will have no problems adjusting in a day or two.

I'm pretty good with my left hand, but can't do too fast aim, or precise movements, I guess that is hard for everyone for their non-dominant hand. Point and clicks, turn based stuff are pretty easy, definitely can work if you put some effort, and mostly time into it. Like a week, and afterwards you can rely on that memory to be minimum serviceable for these games, even if returning months later.
(I pulled my arm when I was writing my thesis. It hurt so much that couldn't use the mouse for more than 30-60 seconds at a time, and thought it's the best if I change up my hands for a while to give a chance for healing.)

It really depends on the person, and if you're left handed, you've got more than a little practice doing this since you've been born.
If the mouse is one of the asymmetric ones (ergonomic...), then it will be a lot harder. Best option is grab another mouse, even if it's a cheap one.
If the mouse has side buttons, those will get hit a lot when you don't want, so I'd suggest turning off or disabling those buttons. If your mouse app doesn't have that function, there are free ones out there that will give you that capability.
As to switching buttons. Righties assume you have to mirror over the buttons, but that's false. For many people it's just as easy, if not easier, to not switch the left/right button functions. Try it for yourself and find out which you're comfortable with.
I'm a leftie, and the only thing I switch is the side of the desk the mouse is on. All but one of my friends that happen to be lefties do the same.
If you're planning to switch hands for some kind of competitive play, just don't. You'll probably never get your alt hand mousing skill up to the level of your primary.
As to wrists getting painful, yeah, it's a good way to get some relief for your primary hand, I had to do that at work a lot. Also look into getting a wrist brace to use. It'll take some getting used to, but it still helps reduce the wrist strain. Put it on BEFORE your wrist starts hurting. If you do it afterwards it just helps reduce further strain, so it's better to prevent as much strain as possible before the pain sets in.
If you're going to someplace, like a college for instance, and they've basically tied the mouse down on the wrong side so it can't be moved to your primary, go and COMPLAIN! About 15% of the populace is left handed, and screwing over either handedness is F'd up! The is NO reason for the mice to be limited like that. It's not like a longer cord reach will result in stolen mice or somebody hanging themselves with it or whatever.
(Sure, it's possible to go all legal on them with that kind of discrimination, but don't. Just point out that you can't use the mouse on the wrong side like that and need it to be corrected. Most people will be willing to help, even if they don't know who to call at first. If you start mentioning legal action however, you just became the enemy and will likely be restricted to only talking with the legal representatives instead of getting the problem dealt with, so definitely not a solution.)

Being a leftie in an 85% right handed world comes with constant issues, even in the computer field. Righties sometimes have to deal with these as well, but usually only due to injury or similar unexpected occurrences. I know I went into this discussion more than most people would have expected, but if you made it this far, thanks, try to follow the advice, and realize that a good chunk of the population has to deal with this stuff on a daily basis, so yeah, we've thought about it a lot.

I had a similar issue and switched from right-handed to left-handed use for the mouse. It didn't take long to get used to that, and helped with wrist pain. Just don't expect to be playing FPS games ever!

I considered (but never tried) a Vertical Mouse for a while, but what is working for me right now (i.e. no pain) is a TKL keyboard and trackball.

Another option is to just use the mouse far less. It's a stupid invention. Learn keyboard shortcuts for everything you can, or use something like AutoHotKey to add your own.

I've never tried with a mouse, but using a track pad with the left hand feels pretty natural so I guess it shouldn't be that hard. Now I'm curious about giving this a try.

I played a lot of fast paced or competitive shooters and still do. When i was younger i never had any pain even after whole day of gaming but nowadays i really need small breaks because my hand or wrist (sometimes my whole forearm) hurts after couple of hours if i push myself too hard (and im not even that old :( ). For this few years i started to use my left hand while resting other one. It's not really that hard to get used to but it's need practice. But of course it's not like my right hand, surfing net or playing turn-based games is fine but doing other stuff than that things impossible for me. Also sometimes i use touch pad with my both hands but it isn't much better than using left hand. [Left hand for pressing buttons and right hand for moving the cursor, it's better than using mouse when my hand hurts.] In my opinion using left hand for mouse easier than using keyboard with right arm. Can't adept my right hand for left side of keyboard. Learning new tricks much easier at young ages but it's feel like after a certain age you are own your own.

I'm left handed but I use the right hand for the mouse all my life but I just tried it and it isn't that bad with the left handeither (of course with switched primary and secondary button) But I just have a plain cheap mouse so no special buttons or something, this would make it more difficult I think.

But overall it's always a good experience (and as I read also good for the brain) to try to do some things with the other hand. Brush teeth for example is something which is quite weird for me with the "right" hand ;)

After decades of constant computer usage, it isn't surprising I've developed wrist strain and carpel tunnel. While I can use the mouse left handed, I am a bit slower using the buttons because I am not consistent with it. (Nor do I configure it for lefties.) However, I have an MMO mouse at home, so that makes using it left handed quite moot. However, some of the things that help with the strain is investing in memory foam wrist rests for my keyboard and mouse. Wearing a wristband on my mouse-using wrist also helps restrict movement and is actually quite comfortable to use alongside the mouse wrist rest.

My wrists hurt every few days from playing too many games, what I would recommend is getting medication that specifically focuses on reducing swelling on muscles. That's what my problem is, the muscles are scraping against each other when I click or type and that causes inflammation, so I got medication that reduces it, so I take that every few days, and then it doesn't really bother me :).

i think u could get used to it just like ur right hand, but i honestly dunno cuz ive never tried.