Update: Tried using a VGA cable to connect to an external monitor and that worked, so I tried the same with the tv and it worked too. So not a problem with video out in general, but specifically with HDMI. But as I mentioned before, the HDMI out works fine on that computer when running windows.
Update 2: Just to confirm, I have tried updating, but it says there are no updates. The OPENGL version is 2.1 Mesa 20.0.4. I also connected through ssh to check the xrandr config. I’m having trouble attaching a screenshot here, but it shows the HDMI1 as connected and lists a range of resolutions etc. So I gather it is recognizing the output destination.
Update 3: SOLVED. Turns out I was just blind. Tried opening the config file on my mac through the shared folder so I could do a search for “HDMI” in Textedit. Found and deleted global.videooutput=HDMI1 (which didn’t show up until I went to Video Settings and changed it from auto to HDMI, then reopened the conf file). Rebooted and it displayed on the TV through the HDMI feed.