I have not been very successful in provoking a black screen on RPiOS.
RPiOS display config app shows 1920x1080 (without trailing "i") and TV OSD says 1920x1080@60.
- Booted up and added disable_fw_kms_setup=1 and rebooted -> black screen.
- Commented out disable_fw_kms_setup=1 and rebooted -> boot to desktop.
- Uncommented disable_fw_kms_setup=1 and shut down, power cycle -> boot to desktop!!!
- Rebooted twice with disable_fw_kms_setup=1 -> boots to desktop every time.
- Power off, wait one minute, power on -> boot to desktop.
- Switched HDMI input on the TV back and forth while the RPi was running
followed by reboot -> blinking cursor in top left corner for a couple of seconds followed by black screen. - Reboot -> boot to desktop.
It seems like switching input on the TV makes it more likely to end up with a black screen after a reboot but it is not consistent.
I've verified that the config is properly applied by running vcgencmd get_config disable_fw_kms_setup. All reboots have been clean, either by the desktop menu or via ssh.
I'm not sure that we've gotten that much wiser. Then I come to think of it, I've been using the 32bit RPiOS so I gave the 64bit a try. The same thing happens.
- Booted up and added disable_fw_kms_setup=1 and rebooted -> black screen.
- Rebooted -> boot to desktop.
I tried a couple more reboots and it seems like the 64bit OS behaves the same as the 32bit.
Any other things I could try?