The procedures for doing so seemed to be unnecessarily complicated and difficult to find when starting, ironically, from a Google search on another device.

Worse, the security policies seemed to be fundamentally flawed, because they kept insisting on some form of authentication based on a trusted device when the purpose of the transaction was to notify them that the trusted device had been stolen.

There has been an unhealthy trend recently of assuming that everyone has a mobile phone and that communications to that phone/number are a good method of authentication, without adequate thought to what happens if the physical device and/or the associated phone number are compromised, or to whether protocols like SMS are really suitable for this sort of application. And some of the really important things, like banks and government services and email providers (which are in practice a gateway to everything else you do online) are often among the worst offenders. I don't know what to do about this, but certainly raising awareness of this kind of problem would be a good start.

Are you suggesting any random person without any authentication proof to be able to just sign people out of their devices ? That would be a broken security.

Another thing that will not migrate phone to phone is Signal conversations if you're inclined to keep those.

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.

-- the more elaborate, the more cool you feel doing it :)