External monitor is stuck at 30hz on HDMI display port

I have a MacPro 16-inch, 2019 with 16GB memory. Running Sonoma 14.0 OS.

The laptop has 4 x USB-C ports.

When I connect an external 4K monitor via an HDMI cable to a USB-C hub to my laptop - I can only get 30Hz display output. This causes mouse lag. Which drives me CRAZY!!!

When I set the display reolution to below 4K (below 1080p) then the refresh rate on the external monitor is available at 60Hz.

When I plug my Linux laptop onto the same monitor - I get a nice handy 60Hz refresh rate on the same USB-C HDMI hub. (Exactly the same HW except the laptop).

When I use a USB-C / DP cable on my MAC, then I get 60Hz

My question: Why can MACOS not recognise or set HDMI 4K refresh to 60Hz, and in the process fix the mouse lag between internal and external screens? While Linux and Windows does not have the problem?