have you successfully installed a custom rom / foss on a redmi 10c?

Here you go pal

Although it's a shame they don't have a vanilla variant for your phone model

Few advices before you start:

• Before unlocking your bootloader be sure to logout from all your account esspecialy google ( otherwise you might get locked out from your device )
• The unlocking process can be a bitch ( The process has a Wait time. )
• Before all that be sure to download your original rom ( also known as R_vendor ) and twrp for your specific device model
• Also note that flashing your rom can be stressful and (in case something went wrong) It might require some time to fix everything up.

Do I still recommend it? Yes.

Edit: if you are locking for a guide i recomend this one

Yes, and you can join R10C telegram group

https://t.me/Redmi10CGlobal

You'll find many tutorials and custom roms

I've done this on a Poco X3 Pro, very similar steps 😃 Just search a bit online and maybe check /e/ os