External display via Dockingstation 30Hz

Dear all,

I have a XPS 13 9310 (Intel(R) Core(TM) i7-1185G7 Prozessor der 11. Generation (12 MB Cache, bis zu 4,8 GHz) with Intel(R) Iris Xe Grafik) from Dec. 2020.

I recently bought a 3840x2160 10bit display (Acer KG282K) that I'd like to connect via a docking station. The problem I'm having is that the refresh rate is limited to 30Hz, and I don't know why.

Help is appreciated.

Some additional information:

- things worked fine on my old 1920x1200 display.

- I've tried with both an old(er) Dell docking station (WD15) and a new Lenovo one (ThinkPad Universal USB-C Dock); the issue exists in both.

- I'm using the HDMI connection of the docking station, and the HDMI cable that came with the monitor.

- The docking station also has other services connected (mice, webcam, ethernet, keyboard), and is supplying power to the laptop via USB-C.

- The laptop is running Pop OS 21.10

Many thanks!