Password doesn’t work after migration assistant

I have just used migration assistant to transfer a Time Machine backup to a different MacBook Air. This is the third time I’ve done it. The first two times I had to completely restore the computer because there is no way to get in. I have not changed my password and I have tried every password for both my Mac (it’s been the same for the last 10 years) and iCloud (I can remember my previous passwords. None of them work.).

I had not associated this MacBook or user account with an iCloud account yet, so I don’t know that there is a recovery option through iCloud.

I have searched other questions in the community and found the standard advice copied below to not be useful. It didn’t work for me:

But first try these simpler solutions:

• Make sure that you're typing the correct uppercase or lowercase characters. If your keyboard has Caps Lock turned on, the password field shows a Caps Lock symbol .
• If the password field shows a question mark, click it to display a password hint that might help you to remember.
• Try to log in without a password. If that works, you can then add a password by following the steps to change your password.
• Try to log in with the Apple ID password that you use for iCloud. If you just changed that password and the new password isn't working, try the old password first. If that works, you should be able to use the new password from then on."

Please help!