Why is my Mac mini showing purple and green colors?

When linking my new Mac M4 mini to my viewsonic monitor I get a dark purple and lime green display. Have tried various adjustments as suggested online and have spoken to Apple helpline, but without solving the problem. I saw a post here with exactly the same issue but from 2022, but no suggestions seem to have resolved the issue. The monitor and HDMI cable work fine with my Windows 10 pc. Has anyone else experienced this problem?

[Re-Titled by Moderator]