Have a Raspberry Pi 4 2Gb
Have a problem when connecting two HDMI monitors (using two official microHDMI leads)
RPi4 freezes during boot.
Both screens (1x1080p, 1x2160p) display rainbow splash screen, then HDMI 2 goes blank and boot process hangs.
(I am also trying to do what others have asked, which is to output to both HDMI ports for Vision in 4K from one, and surround sound via Amp on the other...)