I am using a Raspberry Pi 4b and have tested it with kali linux and parrot os and both come up as 1600x1200 resolution and are locked into that resolution only (4:3)
I made the change you suggested and I was able to display properly; but now I notice a lag on the screen.
I also noticed it is not displaying to a second monitor. When it is, it only shows the rainbow screen on the 2nd monitor. Is there a firmware update that needs to be completed?
I also had a question about the touch screen. What is the purpose of connecting the USB P4 connector to the monitor if the touchscreen USB needs to be plugged in separately anyway?