iPhone 12 Pro, iOS 14.6. Why have events disappeared or have been removed from my calendar

The reason may depend on what your are experiencing:

1. If you are searching for events, iOS and iPadOS won't let you search for events dated more than a year ago. In this case, the only course of action is to use your Mac or PC to search for these events.
2. If recent events simply disappeared, there is no accepted answer out there as to what causes it. Most users don't experience it but some do. There the best course of action is to log on to iCloud.com using your browser, click Account Settings and click Restore Calendars. You''ll be offered several calendar backups to restore from and usually one would choose the most recent one.

It is located at the bottom left of the Settings screen:

I logged on to iCloud.com using the browser on my iPhone, and clicked Account Settings. There is no option for Restore Calendars.