I refer to bug 1816860 on Ubuntu Launchpad My dual-boot recognizes and switches to the second monitor under W10, it seems that kubuntu 18.04 does not recognize that monitor, and does not offer to use it. The results of xrandr and some in /sys/class/drm can be found in that report, where it was suggested to file a bug here for the part of it that it doesn't see any second monitor. I'll be happy to help as far as I can to get my setup running.
*** This bug has been marked as a duplicate of bug 109750 ***
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