Migration Assistant stops, then asked for login as Setup User

So, I'll start with this. I'm a day into being a Mac owner. Here's the problem. I have the migration assistant running on the Mac, and I downloaded the correct version of the Windows Migration Assistant on the PC. They are connected to the same network, and they can see each other. The Mac sends a confirmation number over to the PC, that part works. Then the PC starts searching for files to migrate, which is also good.

This takes a while, so I step over to get a snack, and when I come back the Mac seems to have gone to sleep. Now remember I'm totally new at this, so when I say it seems to have gone to sleep what I mean is the screen has gone black. Not sure what I was supposed to do about that, but eventually I got the screen to come back on. But then it wanted me to log in again, except that it wants me to log in as a Setup User. So that doesn't work, so I power down / restart the Mac. After that any attempt to rerun the migration assistant takes me back to the Setup User login page.

Googling this came up with suggestion to press the control alt command delete and enter keys all at once. Doing that does change the login screen, but still doesn't let me login as myself. So I just rebooted the Mac and left it at that, because I won't need my PC files until I go back to work on Monday.

My work-around has been to just go out and buy a terabyte external disk, completely back up the PC, and then I'll copy the files I want over to the Mac. But it would be nice to know what this Setup User thing is, and how to get past it in case I ever see it again.

Personally, I would start up in Recovery and erase the drive and start over. Since you do not need anything on your new Mac, you can start fresh again. Then you wouldn't have to worry about "Setup User" popping up again.

https://support.apple.com/en-us/HT201314

And don't do anything when/if the screen goes black in the middle of the long migration process. What you probably did was either restart or reset the Mac, which interrupted the migration and left you where you are. If it's asleep, all you need to do is press the spacebar and it should wake up again. You can use the new drive as a backup drive for the new Mac once you are done with the migration.

The OP may have experienced the need to enter a password on wake-up .. generally the default for new machines.

But if it stopped in the middle of migration assistant working, there isn't an account set up for the password yet. On first boot, you are running MA before setting up any accounts. That's how MA can then set up the account with the same information as you had on the source system. I suppose it COULD be requesting a password if it got past the MA stuff and then timed out, but the OP seemed to think MA was still running.

Also, given that the OP has moved on to other posts and threads, it seems this one was sorted out.