Migration Assistant claims download source cannot be used because "may be damaged"
I am trying to transfer data from an iMac running OS 10.13.6 to a brand new iBook Air M3. Both are on the same wireless network, and sitting side-by-side. The Migration Assistant on the MacBook claims that "The selected source cannot be used for migration because the volume contains a macOS or OS X installation which may be damaged". However, I have just run Disk Utility First Aid on the iMac, which received a clean bill of health. How can I proceed?
MacBook Air (M3, 2024)