Join Date: Dec 2018
Location: Tasmania & Europe
My Motorhome: Hymer Classic B584
Thanked 11 Times in 11 Posts
Once Catalina is installed - First create a new administrator user (in System Preferences - Users & Groups) for the new user. Then log into that user. That way you can delete the old profile which will have your Apple ID. The new user can create their own Apple ID, if they don't have one already. If they have one just use that.
Then plug the western digital drive in and move all the files to the users folders where they should go - photos in the Pictures folder etc.
Then I would strongly urge erasing the western digital drive using Disk Utility as Mac format and using it as a Time Machine backup. That's if it is of a suitable capacity to hold all the files (usually the same as the hard drive inside the Mac is ok, but you can go smaller or larger).