Since Outlook doesn't have the necessary keys to decrypt the emails, direct IMAP/SMTP access would bypass this encryption. Here is where Proton Mail Bridge comes into play.

To migrate all your emails from Outlook to Gmail, you'll need to link your Gmail and Outlook accounts, or perform a one-time import.

Add email accounts to Outlook for Mac using the Accounts window. Ever versatile, Outlook for Mac permits associating a variety of email accounts, including those powered by Microsoft Exchange ...

If you cannot add an account in the new Outlook in Windows 11/10, enable the account for New Outlook, clear the local Outlook state, etc.