Hey there seoyeoness,
Thanks for reaching out to the Apple Support Communities. We see you're getting an error that a migration is in progress when you try transferring data to a new Mac. We'd like to get a few details to work out what could be happening.
First, to clarify a few points, is that error popping up on the iMac, or the new MacBook Pro?
Also, when you say you tried reinstalling, are you talking about the iMac, the MacBook Pro, or both?
Did you try a migration at any point before the error started appearing? If you've already set up the new Mac and you're able to log in, it might help to check Apple menu () > System Settings > Users & Groups. Do you see any unexpected user accounts here? Knowing if you see anything here would help us work out if there might've been an unsuccessful migration that led to that alert: Transfer your information to Mac from another computer or device - Apple Support
Keep us updated on the results.
Take care!