Hi, I'm facing the same problem with a different laptop model. I bought recently the S3221QS monitor and I've connected with my XPS 13 9380.

However, I can not set the max resolution 3840x2160 because the system doesn't provide this option. I've already  downloaded the drivers for both devices (laptop and monitor) but still nothing. The max resolution that I get is 1920x1080.

Does anybody know how I will fix this problem?

The last answer I had from the Dell help desk is due to my XPS warranty has expired, such helpdesk could not help whatsoever, which I think it is unacceptable.

Thank you in advance!