User login freeze after Migration Assistant

Here's what's happened. At first, I ran Migration Assistant with a Time Machine backup of my old Mac. I used an external drive. Afterward, when I entered my user password on the M1, the rotating pink jewel appeared and then turned black. I waited and waited, for hours actually, but the computer refused to log in the user. The existing user account in the M1 was one that was created by the guy who sold me the computer. Essentially, it was an account with nothing in it and was created at setup, so that I could operate the machine. This account was OK. Next, thinking that the problem may be with Time Machine, I cloned the drive on the old Mac (using Carbon Copy Cloner) onto the external drive and started my old Mac up from that startup disk to verify that it was OK. When I ran Migration Assistant using this startup disk, the same thing happened: hanging after entering user password. By the way, I wiped the HD on the M1 and reinstalled Monterey each time, because otherwise I couldn't use the computer. Next, I again ran Migration Assistant with the startup disk and transferred everything but the User data. The computer booted up normally and logged in to the account I had created at setup. Finally, I ran Migration Assistant again and transferred the User data. The problem reoccurred; i.e., after entering the User password, the computer hung. The problem seems to be with the User data. I've eliminated all login items and switched to automated login, so no password is now required. I haven't tried transferring the data to the M1 yet, because frankly I'm tired of all this and want some solid information before I try again. Is there anything else you need to know? Any help you can give is much appreciated.

I can't even log in in Safe Mode. If anyone has any insight as to what's causing the problem, I'd be grateful. If no solution is possible, I would like some help with manually transferring passwords and bookmarks.

Here's what's happened with this problem. I contacted Apple Support, and they very courteously spent an hour troubleshooting the problem. In the end, they had me copy the Home Folder from the old system and create a new account with it on the new system. Everything was transferred except passwords in Safari, which I can recover fairly easily.

However, I was curious about what you suggested, so I took an external hard drive and clean-installed Monterey on it. Then, using Migration Assistant, I migrated just the User account from the old system, which I had on another partition on the drive. When I tried to log in to the account, the same problem occurred. There must be some fundamental incompatibility between this account and Monterey.

Anyway, Apple solved the problem.

OK. As long as I've got this thread going, does anyone know how to fix the "An Unknown Error Occurred" problem when I try to log into the Apple Store?