monitor flashes off and on 30 time/minute mac, AR 23

[Quirk]

My primary screen (a two monitor setup) has started flashing off and on when Archicad 23 is being used. At first it was once a week or so, and restarting the computer fixed it every time. Today it started flashing off and on and there seems to be no cure—have both restarted and shutdown mutiple times. As stated above it only happens when running Archicad and only to the primary monitor the other monitor doesn't flash at all. The computer is a mac-mini (late 2014) runing macOS 11.6.1 (Big Sur). Any suggestions will be appreciated.

Thanks