How to add Calendar to Your Phone?

Instructions for individual platforms:

Apple
https://support.apple.com/en-us/102301
Android
- Google Account under Calendar
  https://support.google.com/calendar/answer/37118
- Paid ICSx⁵ app on Google Play
  https://play.google.com/store/apps/details?id=at.bitfire.icsdroid
- A freely available application ICSx⁵ through unofficial trade F-Droid
  https://f-droid.org/packages/at.bitfire.icsdroid/
Outlook
https://support.microsoft.com/en-us/office/import-calendars-into-outlook-8e8364e1-400e-4c0f-a573-fe76b5a2d379