iMessage not Working since update to Monterey with more updates.

I still have not been able to get Messages working on Monterey 12.6.8. !!!

SEVERAL updates have been applied since Monterey released.

When I try to "Sign in to iMessage with your Apple Id" I use my working apple ID and get prompted for a pw.

After I enter the PW, the wizzy thing spins and after about 3 minutes a message appears in red:

An unknown error has occured.

On the same iMac 27" late 2015, I have created a bootable partition on the internal HD, installed Big Sur from scratch and have no issues whatsoever with Messages.

I believe my IOS version was upgraded from Catalina previously to Monterey now.

Very annoying for sure. I have since deleted the BigSur partition to free up space which I need because accessing the internal HD is very difficult (didnt have to be so hard for sure!)

My iPad Apple device works with Messages.

Why cant this be solved by technical support.

I saw yet another thread where others ask the same question and the response alway concerns a device, not an iMac running the latest version of iOS.

PLEASE HELP.

Then after waiting for several minutes, this: