Which only worked if you had both phones working at the same time... I'd bet a sizable portion of new phone enablements are due to losing the previous phone irrevocably.
When doing a factory reset because of whatever reason, this becomes an issue as well. You cannot take screenshots of the bulk export QR-Code on Android because of FLAG_SECURE, so you need to work around that and take a photo of the screen with a different device to import from later.
Also, as of last week, there existed an issue with special characters when trying to import and the app would just freeze or not recognize the QR code pattern at all, so you better had backups of all your secret keys.
Both issues made me switch to Aegis and appreciate my past self backing up the secrets with KeePassXC.
I have long migrated to Aegis and it is pretty awesome. Backups. Copy & Paste. Encryption. Auto-upload to Nextcloud. Better Interface (with names!). etc.
You'd save the QR code at the time you first used it on the old phone, and not wait for when you needed to transfer it.
For me, I'd usually be on the desktop when setting up 2FA anyway, so I'd just save the QR code from the desktop browser ("Save image as ..."). When I needed to set up a new phone, I'd open the saved image on the desktop and point my phone at the screen.
That's an absurd expectation. First of all, many users don't even have or use a computer. Of course, I personally do have one, but I'm often nowhere near one when I set up MFA on a new account. So then I guess I screenshot the QR code to my phone? But if I saved the image to my phone it gets stored in my photos backup anyway. Why would Authenticator not just back its own contents up, to that exact same spot, rather than me doing some crazy runaround that for some reason involves images?