jeffrey writes in reply 6:
"I have used this successfully in the past, but my 2015 MBP and 2023 MBP M3 Pro won't make it happen"
If you mean "setup assistant" (when setting up the new mac), OF COURSE it will still work.
I migrated from a 2015 MBP 13" to a 2021 MBP 14", without any troubles at all.
However...
I strongly suggest that you create a cloned backup of the 2015 on an external drive.
Use that "from which to migrate" the VERY FIRST TIME you boot up the new MBP.
You DON'T want to create a NEW account on the new MBP, and then try to migrate your "old" account over -- you'll end up with TWO accounts and permissions problems.
If you're concerned about applications not working, you can choose to migrate everything EXCEPT applications.
Once the migration is done and you are up-and-running with your migrated account on the new MBP, you can "test launch" 3rd-party apps "one-at-a-time" from the cloned backup, to see if they'll run.
If they do, just copy the app from the backup to the applications folder.
The ancillary support files should have already been migrated with your account.