Hello.
Let me preface this by saying that we understand the feeling for digital sovereignty.
However the mark of american and US digital infrastructure impregnate every system you might want to use to get free from it. In particular, Android being kind of American, you can’t really have a non-Android*
(Just to add in case it’s not clear. Most of the Operating Systems [OS] discussed are derived from Android, whether it be LineageOS, iodéOS, calyxOS, Ubuntu Touch… All these are Android modified, with stuff added or taken out)
If what you meant is you want to get away from google, go for a more open/europe based system, but still android, but where you’re in control of your data and such, I can only recommend /e/OS. If you’re just beginning and want something familiar, this is the go-to. Just search for e/OS from the e foundation.
*as an aside, there is a non-android phone system for fairphone. It’s called sailfish os. If i understand correctly it’s Finnish and is completely from scratch. But be advised, it’s very different and not easy to set up.
But if you want to make a statement, take a stand, you can, this way. Look for sailfish os, from jolla.
EDIT : apparently Sailfish is not available for the FP3(+), only FP2, FP4 and FP5.