Support for Exchange, Outlook, CalDAV, and other Calendars
NotePlan supports all calendars that can be added through your macOS and iOS "Internet Accounts" system preferences, such as Microsoft Exchange, Google, Yahoo, Aol.
If your service is not listed, you can also add calendars through "CalDAV". Click on "Add Other Account..." to reveal this option:
Possible Problems with Exchange
If your Exchange events are not appearing in NotePlan, you might need to complete the MFA (multi-factor authentication) with your organization's systems. Reach out to your IT department or search your intranet's help articles to clarify the process (here's an example).