When I was on LibreELEC I was told I could check “/usr/lib/kodi/kodi-xrandr | pastebinit” to see what different modes my TV and NUC could play, and to see if the TV and NUC played 23.9758 as it should.
Is there a similar way for me to find that out now?
That is an X11 command that would not be applicable on OSMC which is not running an X-Server.
To see the reported modes of the TV you can use grab-logs -P -z