I've had a lot of compatibility issues between my U3818DW and macOS and Dell doesn't care. Even more, their support staff on their public forums don't even acknowledge their buggy USB-C implementation and insists on blaming Apple. [1]
[1]: https://old.reddit.com/r/UsbCHardware/comments/ettgrg/dell_r...
That's a shame. This monitor is spectacular over DisplayPort with my good old 2015 MBP.
Indeed, the image, price and size are spectacular. But this atitude has put me off Dell and they won't get my business anytime soon.
That's true for most Macs, too: people are very prone to believing that their experience is universal rather than a hardware failure or local configuration issue.
FWIW, the monitor I talked about is the standard issue monitor for most employees (~500) at my office. My company has MBPs ranging from 2016 to 2020 of varying sizes and I've never heard anyone say anything negative about the connectivity to their monitor.
https://www.dell.com/en-us/work/shop/accessories/apd/210-arc...