Not knowing what your specific issue is as Strit alluded to above but this may be a good time to post that with the pi4 there are issues (that they are aware of) that with certain monitor's/tv's not getting the EDID info properly from the monitors. In my case it is my VIZIO tv and had to disable gathering EDID all together (hdmi_ignore_edid:0=0xa5000080), force output to the hdmi port ( hdmi_force_hotplug:0=1) and had to manually specify my tv's info. The :0 & :1 in the config lines in /boot.config.txt are for the hdmi port numbers for port 1 & 2 respectively on the pi4 board. You will have to change in the example below the hdmi_mode:1=39 for the hdmi_mode that is for your monitor that can be found here under the hdmi_group=2 section. Also note in my case hdmi_modes 39 & 81 says the same thing for resolution but only 39 will work!
In /boot/config.txt this would manually configure the second hdmi port. Look up and get the correct hdmi_mode for your monitor's resolution and replace 39 with the correct number:
This is an example for the first hdmi port on the board: