3 GPUs, each with one display

Hi, for our project we want to use 3 GPUs and connect one display to each GPU. Currently we use RTX2080, but we want to upgrade to RTX3080 (or 3090?) as soon as possible.
A test with 2 GPUs and a monitor connected to each GPU already fails. The monitor on the second GPU defaults to a low resolution and low frame rate. We can not set it to the actual frame rate of the connected monitor.
We use Windows 10 and the latest nVidia drivers.
What are we doing wrong?