Locked out after migration assistant transfer

try resetting password via terminal > recovery.

1. Shut down your Mac. If you can't shut it down normally, press and hold its power button for up to 10 seconds, until your Mac turns off. (Every Mac has a power button. On laptop computers that have Touch ID, press and hold the Touch ID button.)
2. Press and hold the power button again. As you continue to hold it, your Mac turns on and loads startup options. When you see “Loading startup options” or the Options icon, release the power button.
3. Click Options, then click the Continue button that appears beneath it.
4. Click on "forgot all passwords"
5. enter your Apple account credentials
6. on the top menu bar click on utilities > terminal > type : resetpassword and hit return/enter
7. deactivate the Mac (if the option appears)
8. reset the password and restart the Mac..

viola! the issue is resolved! enter with your new login password

This is Apple’s guidance for resetting your login password:

If you forgot your Mac login password - Apple Support

and if you still can’t reset your password, then see:

If you can’t reset you Mac login password - Apple Support