I use the TOTP option in KeePassXC and KeePassDX to handle 2FA duties. I backup the encrypted file to my Nextcloud. If you self host Nextcloud or something similar this is a viable option.

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.

FreeOTP+ activates my almonds quite nicely.

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

I used Bitwarden for a while because I liked having everything on one app. A bug with their service made me spent a day without my 2FA codes, and if your subscription fails to renew by accident they also lock the codes. Noped right out of there.

I now use Google Authenticator. Nothing special, not going to be the favorite comment on a privacy community… But it works, is free, syncs across devices, is guaranteed to work well on Android. Super simple.