I have a graphic card (3070ti) that won't display if I use a riser to power it up but if I remove the riser and use the 16x slot direct it will display, I have tried variants of risers 006,007 and 009 but same result, I need to use riser so that all other ports can be available for use too, 3070ti is a fat GPU.
First, turn off the PC, then connect the monitor and check the video output. If connected on a running PC, the video output may not work.
For video output, you can use another cheapest video card or use Linux with access through the terminal.