Xrandr and external monitor

[H]

Running the latest version of Rocky Linux fully updated and Mate on a Dell Inspiron 7570 laptop with a UHD display, i.e. 3840 x 2160 pixels. I would like to attach two external monitors and initially experimented with a Dell dock model 3100 and the latest version of the DisplayLink and evdi drivers. However, although the Mate display applet shows the correct resolution for the laptop display itself and for the external monitor which is running at 1920 x 1080 pixels, the resolution on the second, external display is more like 640 x 480 pixels.

While I initially thought this was due to a bug in the DisplayLink/evdi drivers, I see the same issue when I connect the monitor directly to the HDMI output on the laptop itself, ie. DisplayLink/evdi are presumably not involved although they are installed, nor is the dock of course.

I just discovered running xrandr --listmonitors that, while the internal laptop monitor is labeled eDP-1, xrandr identifies the external monitor as using DP-1 although it uses the laptop HDMI-connector. Further, while mate hardware display monitor also identifies it as using DP-1 - possibly based on xrandr output - the monitor itself tells me it is connected using its HDMI1 connector. xrandr does report the correct display resolution, though.

Thus, it looks like xrandr misreads the configuration feeding it to mate. But, I guess it could also be the BIOS perhaps? I just updated the BIOS to the very latest version and saw no difference.

Could this be an X11 bug (I am indeed running X11 and not Wayland)? How should I troubleshoot it?

Appreciate ideas!