In fact, I did a reinstallation where everything looked as it should on the monitor untill I added video=HDMI-A-1:1280x720@60D to cmdline.txt. After that, I got no picture at all, not even after removing that line, so this is the point where I did another reinstallation. I did not try vc4.force_hotplug=1 at any point though.
Hi, What kind of monitor did you use for RPi4 setup, and what is the max. supported resolution? The 720p resolution is something standard for TV's. Something very strange happening with your RPi4 setup. Could be the HDMI cable, was few cases with poor quality HDMI cables what isn't supported higher resolutions (the monitor resolution?). Or the power source, I had something similar with my RPi3, when I connected something to RPi, after reboot wasn't had picture. Or TV EDID detection, could you try with another TV? Or after fresh TV setup, when the screen setup is done, try to send thru SSH the "getedid create" command. That will save the TV display parameters (EDID data) and will use it at every startup.