It didn't work a couple of years ago, at least in Linux, with the open source driver. I don't know what the situation is nowadays.

Fixed in linux 5.5(jan 2020) according to a phoronix article.

That is excellent to hear! I really, really want a Linux workstation using Dell UP3218K. Sadly so few people have this monitor, and even fewer use Linux, that it's quite the financial gamble to know what actually works and what doesn't. I could return the monitor, of course, but then I end up with a newly bought machine without any display I could use...