I have an old DELL P1913 monitor with DVI input, and is connected to the RPi4 using a micro HDMI to DVI cable.
For the monitor to work on a standard RaspberryPi OS image I have to add
With this config in the /boot/config.txt RaspberryPi OS desktop works fine, I can see the screen and use the computer without issues, but that doesn't seems to work for recalbox (I tested with 9.0-64bits and 8.1-32bits) and setting the config directly on the config.txt or in the recalbox user config.
In both scenarios it works but partially, during boot the monitor switches from the proper screen with the proper resolution 1440x900 to blank screen, on and off, so I can see the boot process intermittently.
Later (I assume when emulationstation starts) I see nothing from that point on.