Migration Assistant uses Wi-Fi instead of Thunderbolt on MacBook Air M3 and MacBook Pro M6

Migration Assistant uses Wi-Fi Peer-to-Peer instead of Thunderbolt cable (MacBook Air M3 → MacBook Pro M6)

Setup:

• Old Mac: MacBook Air M3, macOS Tahoe 26.6.2
• New Mac: MacBook Pro M6, macOS Golden Gate 27.0
• Cable: Apple Thunderbolt 5 Pro cable (bought at Apple Store, brand: CalDigit), connected directly with no hub or adapter
• Data to move: about 400 GB.

What I tried:

1. Connected the cable and started Migration Assistant on both Macs. In Connection Details, it picked "Peer-to-Peer" at about 68 MB/s. The only wired option was listed as "Ethernet", sampled at only 37 MB/s, and there was no Thunderbolt entry.
2. Turned off Wi-Fi (forget all possible WiFis) and Bluetooth on both Macs and started again.
   1. Checked System Settings > Network on both Macs. Thunderbolt Bridge shows a self-assigned IP (169.254.x.x) on each, and the port the cable is in shows as Active.
   2. Go to Network.app I cannot find my old Mac Air in my MacPro's Network.app. Just empty. Nothing.
3. Turned off Wi-Fi (forget all possible WiFis) and Bluetooth on both Macs and started again. Once the old Mac entered migration mode, Wi-Fi came back on and the Wi-Fi menu was greyed out. Current connection again showed "Peer-to-Peer". When I unplugged the cable, the transfer kept going, which confirms it was using Wi-Fi.
4. Tried Share Disk mode from Recovery on the Air. The new Mac mounts the Air's disk over the cable in Finder, but Migration Assistant doesn't list it as a source.

Question: How can I force Migration Assistant to use the Thunderbolt connection?

Thanks!