@tripplehelix The problem with seedvault is already fixed. I have a working build here that I would like to share but currently cannot upload anything to androidfilehost because their upload function is broken for me. Contacted their support already two weeks ago but no one replied so far.
So far LOS 20 is stable for me. I upgraded from LOS 19.1 on October 10, which was stable before too. The only issue that all custom roms have currently is that not all features of the camera are usable: Camera & Camera2 API - missing features & bugs
If a limited camera is fine for you, I would say try out an unofficial build. As @Aaanze already said, once the FP4 gets offical LOS 20 support it should be just a matter of running a script to migrate: FP4 and (unofficial) LineageOS - #383 by mmustermann and FP4 and (unofficial) LineageOS - #386 by mmustermann