For quick installation of any mode, I added in (uEnv.txt) the VMODE variable, through which I can quickly set any available mode. During testing, I discovered an interesting phenomenon. If set any 1080p mode, the test monitor does not work. But if I set the 4K2K30HZ mode, when starting the monitor flashes several times and turns on the normal display (1920 x 1080) and begins to work correctly HDMI. Perhaps the reason for the lack of an image with the standard 1080p setting is due to incorrect data that the system is trying to get from the monitor (EDID). Forcing the "strange" 4K mode on forces the system to find the working mode and starts displaying the image correctly.