Welcome to the community 
LOS for the FP4 is in a constant state of almost released, but there is a bunch of different ROMs available, have a look at the oslist
The FP4 is very much permanently brickable, you"ll find quite a few stories on this forum of people successfully turning their phones into a 
If you aren’t careful, that absolutely can happen.
Android kernels are usually pinnend to a specific version, based on your hardware, it rarely happens, that a OEM bumps that version to a new major release.
There is however ongoing work to get a mainline kernel working, but that will still take some time.
The wide angle lense is the biggest problem at the moment, and in general some proprietary camera stuff. Some of it hopefully get’s resolved when the phone finally gets upgraded to A12.
Other than that, it’s mostly the same, since custom ROMs ship with proprietary blobs / firmware included.