GOS = Easy to super easy
Linage / other on Samsung = hard
In the past other roms on devices have caused issues for me (I'm happy to deal with them) and others (who would prefer to just use google).
I understand you want the best for your friend, but if there already immersed the best experience for them is just default samsung.
It would be better IMO to format, debloat, and then install some privacy friendly options.
- FDroid
- Thunderbird / Email client of choice
- signal
- browser of choice
- etc
That way they have some privacy apps to get started.