I’m familiar with projects like them. I just don’t think any of them are going to break through in a meaningful way anytime soon, if ever. They have very niche markets. I hope they are always an option though.
The prospects for growth are better than ever. GrapheneOS by installer download stats looks to have approximately a quarter of a million users, and the new Motorola partnership should cause that to increase significantly.
Graphene is still tied directly to Android and Pixel devices. It is always at risk. Good luck if Google decides they don’t like the project enough. I went through that nonsense with Canon and magic lantern years ago. Firmware 2.3 was specifically designed to break it on all DSLR’s
I researched a phone which should work with lineageOS.
When I received it, I had to find some archaic website and _ask permission_ from a vendor to have the phone unlocked.
From there, I tried to image it from adb and using "guides" (ie, forum posts) and nothing that worked for everyone else ever worked for me.
On paper, installing an aftermarket OS on a phone is not much more difficult than installing an aftermarket OS on a computer. In practice, it's incredibly frustrating and a bit of a crap shoot.