Can I migrate a specific file from my old iMac applications folder to my new Macbook. I want to be able to pick and choose the files I migrate.
Migration Assistant is quite flexible in some ways but not in others. In the case of applications you must either migrate all or none.
You are given "some" choices but they are limited How to move your content to a new Mac - Apple Support
As a rule, you can't just copy an app from one to the other. Most apps have supporting files spread in various locations.
Can I go to "all my files" and copy all the files for the application that I want to migrate. Will this work?
"All My Files" only contains document files. Not Application Support files.
applications bought in the App Store can easily be downloaded again when signing in with your Apple ID
Migrating files from old iMac to new macbook
