How do you store seed values in password managers? More specifically: how do you export them from Coogle Authenticator? (I’ve not found that option). And how do you import them again?
To store the seed values, simply store the text provided for use if you can't use the qr code.
There would be problems on fully-isolated systems experiencing clock drift, but on any modern Internet-connected system using NTP or on any cell phone with time synced to the network it shouldn't be a factor. The most likely problem scenario is probably a corporate network using only an internal time source that drifts.
Doing a single code as validation only makes sense to catch transcription errors since in case of problems someone could end up locked out of an account.
Another thing that will not migrate phone to phone is Signal conversations if you're inclined to keep those.