What i don't understand is, why Proton Authenticator, which can also sync your 2fa accounts to Proton servers, does not have a separate password (from Proton Pass.)

So anyone who gains access to your Proton Pass account credentials, automatically gets access to your synced 2FA codes too

And obviously you would want to enable syncing your 2fa accounts, in case your device gets stolen / broken / etc.

So the only solution seems to use another 2FA App from another developer.

https://proton.me/authenticator