Migration Assistant fail and left over 100GB on system data, Now there is no space to try Migration Assistant again

WiFi isn’t fast enough for Migration Assistant. I really wish Apple didn’t make it an option. Many years ago I tested the various ways one can migrate and my favored solution is unchanged all these years later. Back up your old computer using TimeMachine and then use the TimeMachine backup to migrate to the new computer. It not only is the most reliable method but simply put, everyone needs at least one backup drive so this method kills 2 birds with one stone. 1) you get a backup you can rely on and keep using on the new computer, and 2) you get a fast reliable means to migrate.

The best way to proceed is to wipe your computer and start over. The Apple Knowledgebase article describes how to prepare your computer for resale. You can skip down to step 6 and then step 7. Then you can try using MA again but not using WiFi.