Migration Assistant stuck after selecting startup disk

Hi,

I am trying to use the migration assistant to transfer files from and old to a new Mac. However I would like to use the thunderbolt3 cable. I connected the two mac's using the cable and set the old as target using the method described here https://support.apple.com/guide/mac-help/transfer-files-mac-computers-target-disk-mode-mchlp1443/mac

I started up the migration assistant one the new, selected the startup disk and clicked "Continue". It got stuck there and did not continue the process. What else should I do?