I recently tried to import and old backup which contained a key I thought was obsolete. But didn't have any luck. My up to date authenticator couldn't read the 2 years old export.
I've very hastily made sure that all my backup keys are up to date afterwards...
Fair enough. I stopped using it right around the time (~2 years ago?) when they finally added the ability to do an export. At that time, the compelling reason to use alternative TOTP apps was the ability to sync the secrets. I assume this feature was driven mostly because of said alternatives, rather than goodwill for such a simple/obvious feature.
I always did & do save a copy of the QR code or, if provided, the BASE64ed key in my PW manager. I know I'm never locked in with TOTP: I can use anything (I've written the 10 lines of code, even) to generate the code, and it can be entered manually on any device that can display the site's login page by hitting 6 digit-keys. WebAuthn needs, at minimum, the browser to remain open to integration.
Not op, but my qr codes & strings are saved in a separate keypass database, saved in a different location & using different password (saved in my brain only).
I've very hastily made sure that all my backup keys are up to date afterwards...