It has a countdown timer and a threat, which screams scam.
Yes, it’s a scam.
Somewhere along the way, you were likely offered a calendar subscription whether in a mail message or on a website you’d visited, and accepted and added that calendar subscription offer and now you are getting calendar alerts. Spam-filled calendar alerts.
Follow the earlier-versions section of the following to remove the calendar subscription.
See this link > Delete spam calendars and events on iPhone - Apple Support
If this is the subscribed calendar as seems likely, your iPhone is fine, there is no malware here, no infection, nothing wrong.
See this link > Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support