As I didn’t find an option for 2FA in Monero GUI, I created my own way:

By using the HMAC-SHA extension of FIDO2 Tokens, my script generates a symmetric key with which the wallet-files are encrypted.
So now one need the FIDO2 Token and the wallet password to access it.

PS.: If one of you knows a community where people can self-promote their projects, I would be glad to hear it. Because I think the keygen-script can be useful for other usecases.