sorry for the extremely late answer. i bookmarked this and kind of forgot it for a while...

yes, that was me. ^^ i have a 21:9 screen for 3-4 years now. and i love it. don't ever want to go back. but of course there can be issues with some games. overall i would say i don't have a lot of issues. but it's not completely avoidable. it also depends a little on what kind of games you play. i will try to break it down:

• modern western AAA games: almost no problems. i can't remember the last game of this category that didn't have 21:9 support. i usually buy those without even checking. this includes shooters, but also 2D/2.5D games like Stellaris or Civ.

• modern asian AAA games: asian companies usually produce bad PC ports, and that usually also means no 21:9 support (there are exceptions, of course - Nier: Automata had support, surprisingly, even if it was not perfect). there are often user fixes. but generally you can assume they won't even think about implementing 21:9. even the big ones like Dark Souls 3 or Nioh don't have support most of the time (but there are easy fixes for both).

• indie games: a surprising amount of indie titles has 21:9 support. i am baffled how big companies like From Software don't offer different aspect ratios for their games, and small studios with just a few guys have perfect 21:9 support out of the box.

• 2D platformers: we have to differentiate between scrolling and non-scrolling titles. non-scrolling games are obviously designed for a fixed aspect ratio and simply can't have any descent ultrawide support. best example is The End Is Nigh. the screens have a fixed size. it makes no sense to even think about implementing it. these games are fixed 16:9, and i am very fine with that. scrolling games are a different story. they should definitely support 21:9, and many do - well, and many don't (and i can get a little angry if a game should support my screen, but doesn't ^^). Ori didn't support it in the original version, but added it in the later version. Sundered has flawless support. Dead Cells doesn't have support, Little Nightmares doesn't either. Nex Machina didn't have it, but added it a few days after release (not really a platformer, but i wanted to mention it).

• racing games: most racing games have flawless support. i have Forza Horizon 3, NCG: Wreckfest, Project Cars, Assetto Corsa, Redout, several Trackmania titles, DiRT 2-4 and many more. i think they all supported 21:9 without problems.

• old games: this is definitely a problem, if you insist on 21:9. many old games will not support that. there are of course exceptions. the original Devil May Cry 4 has support (have to activate via ini edit), while the new version doesn't. asian devs again... ;)

to sum this up: i have very little issues over all. but you have to be prepared to go on the forums and look for a fix for certain games. in most games it is very simple. either download a fixed exe, or edit your own exe file with a hex editor (you usually have to replace a certain value, which takes a minute at most). and also keep in mind: 21:9 means that you get something extra on the sides. it's no big deal if you have to play a game in 16:9 from time to time. i have a 34" monitor (which is the standard size for ultrawide), and whenever i have to play a game in 16:9, it's not worse than before - it's basically like a 27" 16:9 display then. and for all other games you enjoy enhanced peripheral vision. my opinion: after you get used to it, you don't want to miss it - which is what most 21:9 users say.16:9 actually looks quite narrow for me now. ^^