i have the Dragon breath gene but when i'm pressing H, nothing is happening.

I remembered having used it, but obviously I didn't after upgrading, it does not work even after a fresh injection.

same, this happened since 1.22 for me. i just figured i was doing something wrong - like shoot fireballs requires blaze rod...

Me too. And i tried using End Rod but still didn't work

others have said it works, so i just guessed something wasnt documented, and i missed it in testing...

Did you check for key conflicts in the options?

Yes and i changed it to another key but it still didn't work.
Have you tried it in your world in version 1.25 ?

I too checked key conflicts - was my first stop. There were none, but I changed it anyway and still didn't work either

Fixed in 1.26, also reset cooldown to 5 seconds.