Can i check the steam key is used or not at HB

Not revealed would mean not used as you have to reveal a key to use the key in steam right?

If you didn't reveal them, then the keys should be valid.

If a key is unrevealed, it's supposed to be unused because you cannot have seen/used the key till the moment you revealed them.

There is no option to hide the keys once you reveal them at HB, so your keys are unused if they are not revealed.

I heard stories before of people having revealed and used a key and months later, they key was unrevealed again and no idea if it was used or not, I think when revealing they got a new key, but not 100% sure anymore so can't help you there.

High chance to see "Keys are temporarily exhausted for this product" on reveal (or if winner will try to activate gift) - I have 2 keys in that state for ages.

i had revealed keys before and after sometime they were "unrevealed", i think it was a bug
as the key were the same as the one i activated

Mine sometimes still show as unrevealed even though I know I revealed them XD I'd generally advise to getting rid of the key you don't want for yourself asap, I have something from a year ago that they still have no new keys for XD

Happened to me in the past too...
In my case it was due to Chrome caching of Humble site.
Reloading/Refreshing the site helps (i.e. reveals all the revealed keys, even if they appeared hidden before).

I have a key of pre-purchase bonus in this case. I don't know if it was unrevealed or replaced.

I've had Humble hide keys again that I used. I don't know what caused it.

The last time I remember it occurring was a couple years ago.

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Are you suddenly deciding to do giveaways? You should ;)

The only time that happens to me is when I reveal some Humble keys and then refresh the page shortly thereafter, sometimes they show up as being unrevealed. But usually waiting a little bit, refreshing, or using a different browser to check always shows me what is already revealed.

One thing I would suggest you check is your activated game time:
https://store.steampowered.com/account/licenses/

and compare to your Humble purchase dates and see if they correspond. I know this doesn't work for a lot of people, since a lot of people decide to activate keys a lot later, but at least it may give you an idea.