Updated Mac Mini, hdmi display shimmies after log in.

I use my Mac mini to stream video to my Panasonic AE900 projector using the hdmi port. After updating to Monterey, the display, which had been working fine before updating, looks fine on the login screen, but once I log in, it gets fouled up (doesn’t align properly, the bottom is cut off, and there seems to be two images of the same thing misaligned and flickering over each other).

Since this does not happen on the log in screen, I believe something is fouled up in the start-up procedure after login. The display is almost impossible to use and makes you feel like it will give you a seizure.

I have hooked up another monitor to the display port and found this temporarily addressed the problem on the projector, but caused the video from the streaming service not to be visible. Disconnecting the alternate monitor made the video play (there is a problem also with the audio not playing, which I think is a different issue but also related to the update to Monterey). But since the initial success in eliminating the fouled screen by just hooking up an alternate monitor, I now only get a proper image from the projector on the login screen, and sometimes that can be fouled as well.

The small alternate display works, so I have been trying many things to address the problem, with no luck. I tried many variations of display settings and mirroring, color profiles and what not. I don’t believe this issue is the same as the screen flickering many people get, and I don’t even know what else to try.