I have my calendar coming up with warning messages

Delete spam calendars and events on iPhone

If you get unwanted calendar invitations or event notifications, you might have accidentally subscribed to a spam calendar. To remove the events, delete the calendar subscription.

How to remove calendar spam on your iPhone

1. Open the Calendar app.
2. At the bottom of the screen, tap Calendars.
3. Look for a calendar that you don't recognize. Tap the More Info button  next to that calendar, then scroll down and tap Delete Calendar.

If this doesn't fix the issue, delete the calendar subscription in Settings:

1. Open the Settings app.
2. Tap Calendar > Accounts. Or if you use iOS 13, tap Passwords & Accounts > Accounts instead.
3. Tap Subscribed Calendars.
4. Look for a calendar that you don't recognize. Tap it, then tap Delete Account.

https://support.apple.com/en-us/HT211076

This link is provided here much more detailed information about what might be experiencing. I’ve actually seen it happen quite often lately. Remove calendar in your settings.

https://support.apple.com/en-us/HT204759