I have similar problems with using my LG OLEDB6P 4K TV as a monitor. The nouveau driver seems to be confused by the EDID information. Using X it picks some resolution the monitor can't even display (invalid signal on monitor), using wayland I thought it worked, but when I examined the details it picked a strange resolution that the monitor could display, but wasn't the native 3840x2160.
When I switched to the nvidia binaries from rpmfusion it sees 3840x2160 in EDID as the best resolution and displays it no problem.
I have this feeling someone has been "improving" the EDID detection in the open source video drivers.
https://bugzilla.redhat.com/show_bug.cgi?id=1648608
https://bugzilla.redhat.com/show_bug.cgi?id=1575391
I think this started back in fedora 28, but I only recently dug into it in more detail and added info to that first bugzilla.