Hey there SInger2355,
Thanks for reaching out to the Apple Support Communities. We understand you're having issues with the Calendar app not working as expected, and we'd be happy to look closer into what's going on.
To get started, are you experiencing this issue with your iCloud calendars?
If so, we'd recommend taking a look at the following support article for suggestions to check to recover the entries. While we understand you may not have accidentally deleted the calendar events, the steps listed in this article can help.
If still having issues after those steps, give this additional resource a try: If your iCloud Contacts, Calendars, or Reminders won’t sync - Apple Support
Best regards.