How to move archived Outlook for Windows Files to Apple Mail?
Sorry Kevin, but Apple Mail doesn't support Outlook's .pst or .ost files; there's no direct way to import them into Mail.  There are, however, 3rd-party apps that will convert the files for you.

A quick search did turn this article up: https://www.macworld.com/article/2151263/importing-windows-outlook-messages-into-apples-mail.html

which may be useful to you. 

Good luck!