That is very helpful, thank you. So when I see on the Fairphone 3 page “e/OS build version: S (stable)”, this means that the Fairphone 3 can run e/OS if the phone has Android 12 (AKA Android S).
On this same page, I can see how to update e/OS (and also advice here, but not how to upgrade from Android 10 to a later version. Or do both e/OS and Android update together (which is kind of suggested by the link from urs_lesse above.