I can see two issues:
1. The 4K monitor is not plugged into the Nvidia card. Is that right?
2. The Radeon GPU it is plugged into is refusing some modes (because
they're out of range?):
[ 18.036] (--) modeset(0): HDMI max TMDS frequency 300000KHz
[ 18.036] (II) modeset(0): Not using default mode "3840x2160" (bad mode
clock/interlace/doublescan)
[ 18.036] (II) modeset(0): Not using default mode "2560x1440" (bad mode
clock/interlace/doublescan)
So make sure the monitor is plugged into the correct HDMI port. And if
it still doesn't work then please try a different HDMI cable. You will
need an HDMI 2.0 cable to achieve those modes.
** Changed in: xorg-server (Ubuntu)
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1870637
Title:
20.04beta: Cannot set 3840x2160
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