If you are using ProtonMail, you might want to check out their Proton Calendar. Still waiting for Proton Drive (beta) apps to see if it might partially replace Google Drive or Dropbox.
I've been looking at their other services but for now I'm happy using NextCloud, which provides more than just calendar and file storage. I also have phone tracking (so I can send my real time location to my relatives when driving and visualize the places I've been) and an RSS aggregator. Additionally, I'm not locking myself into another service provider. I'm still open to the idea of moving to another e-mail provider some day even though I'm happy with ProtonMail's service so far.