HOw to upgrade my Fairphone 3?

I own a Fairphone 3 that runs on Android version 9. More precisely: /e/OS 0.23-20220406176461.
The latest update is from April 6, 2022.
What is the wisest thing to do? Which version “should” I update my phone to? And (just as importantly) where can I find a guide on how to go from Android 9 to Android 10, 11 or 12. Linked to that is the question: How do I make a good backup of the data on my phone? I can’t find that anywhere.

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.