Question :
In a SQL server 2012 to SQL server 2019 migration, is it recommended to migrate the databases first or the logins first?
Answer :
It shouldn’t really matter as long as you accomplish both correctly. If you’re going to use a backup of your master database to restore to the new server, as the way to transfer Logins, then I’d probably recommend restoring that database first anyway, just to ensure if any subsequent changes to master occur in your new server, they aren’t lost.
Also, after you’ve migrated everything over, you should verify you have no orphaned users otherwise you can resolve them per the linked Microsoft docs.