@shadoom I don't use amiberry so I can't say. You can try installing sdl2 2.0.20, install the wip audiosettings from cmitu's repo (it adds the option for hdmi audio) and then install amiberry again. Retropie's default is 2.0.10. I believe .20 was causing problems with some games but I mainly use libretro cores so it doesn't affect me.
Checking retropie's sdl branch, you can experiment with versions .16 and .18 though I don't know which version fixed the issues with bullseye.
I'm totally happy to do some extra installing/building if that would help.
If I build SDL2 from source repo, would I be able to fix this up without too much editing of cmake files etc?
(i do need to use Bullseye unfortunately)
I think long term, it's much better for Raspberry Pis to have a) an open source graphics stack, and b) a more 'standard' solution. as an educational tool it seems silly for the pi having bespoke APIs, and it meant that (as above) several pieces of software ended up being tied to that bespoke ecosystem out of convenience/necessity.