My new iMac freezes halfway through booting up

Good question. I suggest doing a computer restart in the Internet Recovery Mode. Hold down the Option + Command + R keys on restart to install the latest operating system that is compatible with your Mac. That should fix the problem. Good luck.

When a computer freezes up during startup that often means that the operating system is corrupted and needs to be reinstalled. If you used Wi-Fi or a network to do the migration, that could be the cause.