Driver support needs to be done separately for each device, so it's a moving target. Work on Fairphone 6, a pretty new device, seems to be progressing well.

As far as I can tell Ubuntu Touch, Sailfish and postmarketOS are all daily driver ready. In pmOS you typically have the choice between GNOME and KDE, both of which seem to have their fans, meaning there are at least four relatively mature mobile desktop environments.

The biggest problem as far as I can see is app support, which is not a problem of Linux phone development but of monopolistic and/or careless third parties. And even for that Android emulation seems to have gotten pretty good.

I'm not sure what you assumed and how it fails to align with reality, but Linux phones have had camera support a long time. It's just that it needs to be added separately for each device, each time by unpaid hackers who bought the devices for their own money.

It's a great question. When degoogling my android phone camera quality was one of the biggest initial hurdles, currently resolved because Fairphone offers their native camera app to /e/OS. FOSS camera apps for Android sadly do not have competitive picture quality at all.

As pictures are important to me I could absolutely see it being one of the main hurdles when making the change from /e/ to proper Linux on my phone. I should probably find a way to preemptively start donating to the GNOME camera app.