I've been using KOrganizer[1] for longer than I can remember. For better and/or worse, it's pretty tightly integrated with the Plasma desktop. For now at least, I use it with Google Calendar as its backend. Every once in a long while, it gives me some scary-sounding error message about failing to sync — but so far as I can tell the sync works just fine, albeit sometimes with a bit of lag.
I recently also started using it with my work-mandated Office 365 calendar. According to some docs somewhere that I can't find right now, there were quite a few hoops to jump through to make that read/write so I settled for read-only.
I recently also started using it with my work-mandated Office 365 calendar. According to some docs somewhere that I can't find right now, there were quite a few hoops to jump through to make that read/write so I settled for read-only.
[1] https://apps.kde.org/korganizer/