A notable mention is https://ubports.com/en/ which is different from postmarketos in a sense that ubports uses old kernels with heavy patches. That means: good support for things, but difficult future.
PostmarketOS uses the newest kernels and tries to integrate their patches into mainline kernel, so that the reliability is maintained with all kernel developers.
It’s worse. Linux desktop is only possible because of the relative consistency and openness of x86 PC hardware. Phones are nothing like that. At best we will have retro Linux handhelds with phone functionality.
There’s x86 socs. You can buy a linux tablet right now.
Yes the HW isn’t comparable to a modern phone though.