I use Davmail to talk to O365 and present standard interfaces like imap/caldav/smtp/etc and then use vdirsyncer to pull down my work calender to use with khal. It works pretty good for me, especially now that Davmail does MFA internally so no account changes are needed in O365

Interesting. Does DavMail support creating new calendar events or modifying existing ones and syncing them back to Office 365?

interesting, thanks for the information, I'll give that a go.