When Migration Assistant does not connect

Connect your old Mac's Time Machine backup drive to the new Mac and Migrate from it.

see > Transfer to a new Mac with Migration Assistant - Apple Support

If you do not have a Time Machine backup of the old Mac to use for Migrating.

make one as per > Back up your Mac with Time Machine - Apple Support

Then use that external drive to continue backing up the new Mac.

Migration Assistant does not work between an iPad and a Mac. What are you trying to migrate and to where?

Please follow the steps in Setup Assistant and Migration Assistant. Using WiFi is unreliable and generally is not recommended for a migration. Use the information in the link and your migration will be fast, secure and reliable!

Migration Assistant will work perfectly if you follow the steps I provided in my first post, it NEVER fails.IFyou go off on a tangent expect a complete mess.