LineageOs compatible with European (H850) version of LG5 The "Downloads" page of LineageOS only lists the US version (H830) for the LG5.

Given that they apparently use mostly the same hardware, am I safe to assume that a build of LineageOs that works on H830 will also work on H850 (usual caveats about custom roms applied of course)?
The difference in baseband is often quite crucial - your link isn't showing the bands these models support. This usually warrant separate codenames and builds, although they might be unified in the future.

Given that even unofficial builds for these 2 models still opted for separate codenames instead of a unified build, it's obvious that at least at this moment you shouldn't treat them as one.

You could just use the unofficial builds for now, but shifting back to official builds after that will require a wipe, due to official builds claiming "incompatible data".