Screens turn green when connecting VGA beamer

When connecting a somewhat older beamer through VGA (using a general USB-C - VGA connector), both displays (beamer and laptop display) turn green. Applications are still visible with a strange coloring, and some flickering is going on.

When disabling True Tone, the green turns into a combination of pink and green, where the greens on the laptop are pink on the beamer and vice versa. I have tried several resolutions and display profiles, but none of them brought back the colors as they should be. Using another USB port on the laptop made no difference.

Replacing the Mac with a Windows laptop (HP Probook) using the same USB-C - VGA connector: no issues at all, colors show just fine. I'm not sure what the use of this Mac "feature" is??

After disconnecting, almost all colors have returned to normal, except for the dock: it keeps its strange coloring. See attachment.

This forum seems to contain some similar questions, but these are all very old. Some replies refer to this page: https://support.apple.com/en-us/HT201177 , but it seems to be useless for this issue.

Does someone know what is going on?