I have a home server with an integrated graphics adapter (it's some Matrox G200). But I need to drive a 4K-display with it (amongst other duties), so I've installed a GeForce (GT 710).
I'm toying around with 20.04, and I've found that while during the bootup-/BIOS-phase both outputs have a signal (the Matrox is connected via DP/HDMI adapter; the GT 710 via HDMI directly; cables and adapter are tested and known to be working), but once the system's up, only the one on the Matrox seems to be working. Both cards are recognized by the OS; I've even managed to have both "llvmpipe" as well as "Nvidia GeForce GT 710" show in the "About" window of Ubuntu (at different times, of course). But I have yet to get the GT 710 to properly display a 4K signal.
How can I switch to the "other" graphics card for video output?
It feels like the OS is "stuck" on the Matrox card and is not using the other one at all. As if it's a misconfigured multi-display setup with either mirroring (thus it cannot show a 4K signal since not both cards are able to) or "disable second display" active. Unfortunately, there's not much to be found except for the "Display" settings (which … doesn't even show the two different cards).
All I could find in the forums was about the Intel iGPU and Nvidia Prime; but that doesn't help in my case. I've tried both without and later with the proprietary Nvidia drivers installed. I even tried to disable the integrated (Matrox) card in the BIOS – but then I got all sorts of really strange behaviour…
