I have the 4k XPS 15” from 3 years ago running Ubuntu, which I have been very happy with.
The biggest issue I have is poor support when using Linux for the 4k display. So many niggles and problems with the Retina display and I have tried a variety of different workarounds, and I still have quite a few unresolved issues. I personally wished I had bought the 1024p display. Currently I am fighting with trying to upscale Wine and there is no simple solution - meanwhile the fonts and everything for the application I am trying to run are so tiny as to be unusable (Aside: the Wine Display Configuration text size setting does not help).
Apart from that, the XPS has been a solid performer running Linux with no noticeable software issues. The firmware is still getting patches through Ubuntu which is impressive.
The one persistent niggle with the XPS range is that there is a “coil whine”, which sounds exactly like a tinny speaker tuned to the CPU usage. It isn’t loud but if a noticeable annoying noise drives you insane then be very careful before buying an XPS. I would hope they have fixed the problem, but it had been an ongoing problem with previous models for years, so caveat emptor.