Click on the link to read how to...
Move your content to a new Mac - https://support.apple.com/HT204350
Migration Assistant copies all of your files to your new Mac so that you don't have to copy your files manually. If your files are currently on a Windows PC, follow the PC migration steps instead. If your new Mac is using OS X Mountain Lion v10.8 or earlier, follow the Mountain Lion migration steps instead.
February 2019 tips recommending using a Time Machine backup to migrate to a new computer
https://discussions.apple.com/thread/250194717
Feb. 2021 tips by rkaufmann87 about Setup Assistant vs. Migration Assistant on startup.
https://discussions.apple.com/thread/252408959?answerId=254544151022#254544151022