The support for larger numbers of monitors and mixed resolutions and odd layouts in KDE vastly improved in the ubuntu 23.04 release. I wouldn't install anything other than the latest LTS release for a server ( and generally a desktop ), but KDE was so much better that it was worth running something newer with the short term aupport on my desktops.
We aren't too far off the next LTS that will include that work anyway I guess. I'm probably going to be making the move to debian rather than trying that one out though.
If you go back a bit further, multi monitor support was just fine. Our office in about 2002 was full of folks running dual ( 19 inch tube! ) monitors running off matrox g400's with xinerama on redhat 6.2 ( might have been 7.0 ). I can't recall that being much trouble at all.
There were even a bunch of good years of the proprietry nvidia drivers, the poor quality is something that I've only really noticed in the last three or so years.