TBH I haven't done anywhere near enough research to really know the viability of each of the options mentioned, so I'm wondering:
Replicant - how much does it free you from proprietary g services as opposed to just the code?
UBports - Is it actually basic feature complete or still alpha?
PostmarketOS - isn't this more just a low level base? Does it actually have userland apps?
PureOS - Is this available on any device before the LibreM 5?
It takes #LineageOS (formerly #CyanogenMod) and strips out any remaining nonfree code. Which is why it runs on fewer devices and needs a wifi dongle. #FDroid is the default app installer. Out of the box, it contains no support for proprietary Goggle apps. The user can add any Android compatible stuff they like, but if you want to use some nonfree code, might as well stick with Lineage.
I don't know much about this project yet. But my impression is their goal is get a standard GNU/Linux base system running on an Android device, which can then be used with #GNOME, #KDE, or any other DE that has a touchscreen version. I presume they will supply ready-to-use ROMs with these for each device they liberate.
Linux Geeks doing what Linux Geeks do..