How can I change the default programs that open Outlook email attachments?
I found the answer when reading this post.

Choosing Always Open With in the Open With -> Other... for one file applies this default application ONLY to this file and it is not a system wide setting. To update the system default application for all files with a certain extension do:


open the Finder context menu item Get Info
in the Open with section you must select the application to open this file with
to apply this setting for all other files with the same extension, there is the Change All... button below the application dropdown.


The confusion might be made because in Windows in place of the Always Open With MacOS option, you have the Always use this app to open .ext files (where ext is the extension of the file).