I use the open source BitWarden password manager as a self hosted service and I am using its otp feature as it is really handy

keepass (xc/dx) and aegis

For iOS I use Raivo. https://apps.apple.com/us/app/raivo-otp/id1459042137

I use Aegis, which automatically backs up with each change to the database to a folder that gets synced to a couple of different computers via syncthing.

For backup codes, I have a separate keypass database that’s backed up to a couple of places. I thought about using Bitwarden for this backup, but having my 2FA backups in the same place as my passwords kinda defeated the point, IMO.

Anyway, this system has worked well for me.