I faced the same issue with a Pi 400. It looks that the issue is specific with the resolution and the second HDMI2 port. If I boot the system with the default resolution everything is fine. If i change the resolution to CEA 4 (1280x720 60hz) then a black screen appear instead of Emulationstation.
To be sure, I try to a second RPi4 and in a different TV and the same issue occured.
So if someone have the same issue, the HDMI 1 port for Rpi4 is near to power cable and in the Pi 400i is near to SD card slot or leave the default resolution if you want to use the HDMI2.