Hi Solyom2 try setting your display resolution through your GPU and not your desktop display I have a nvidia 1650 you must have something similar to the nvidia control panel for your AMD Gpu
Also when you installed your new AMD Gpu did you just install the driver cd software if so i would go to the AMD site and download the lastest drivers for your GPU.
AMD Drivers site
https://www.amd.com/en/support
Hope this helps Solyom2