Display on X8 unpredictable

Hi,
I am trying to create a GUI for the portenta and i ran into the following issues:

Using a 720p HDMI screen and USB to HDMI converter:
LVGL demo runs on H7,
nothing is displayed when plugged into X8.

When plugged into 4K DELL monitor:
LVGL demo runs on H7,
X8 shows very distorted image, one can guess the arduino logo.

when plugged in to colleagues docking station:
LVGL demo runs on H7,
nothing is displayed when plugged into X8.

What are the specific requirements when using USB-C to HDMI? Can you name a converter that works out of the box with the X8?