I've uploaded RPi4 builds with the latest version of popcornmix's patch https://github.com/raspberrypi/linux/pull/5052
LE10: https://www.horus.com/~hias/tmp/libr…054-eb85a9e.tar
LE11: https://www.horus.com/~hias/tmp/libr…608-bbb7ee2.tar
Please test with vc4.force_hotplug=3 added to the end of cmdline.txt and report back if this works.
The value 3 forces HDMI hotplug on both HDMI ports, you can also use 1 to force it only on the first HDMI port or 2 for only the second one.
so long,
Hias