are you on -dev or -stable builds? (see howto find out)
A good post on upgrading from Pie is I "upgraded" (flashed WITH dataloss) my FP3 from /e/-0.23-dev-p (Android 9) to /e/-1.5.1-dev-s (Android 12) and here is how - it basically says “backup” (because data loss on-device) and “sideload”. Now the dataloss can be disputed if you’re the tinkering kind, but most people aren’t.
Make sure your contacts / calendars / notes have a remote (cloud) sync, so when entering the account again after upgrading you’ll have that data back. Photos/Videos you copy from the device, and for the Messenger archives you have to consult their guides if you care to conserve this.
I used to test the upgrade route from major to major version, helped solving bugs, and for some versions it’s possible (10->11 when I looked at it). But ultimately it’s not as robust as you’d wish, and you’ll do a Pie->S (12) jump, that I think is rarely tested.