It’s spam with calendar invite entries.
Those get accepted or rejected. Not deleted. And accepting or rejecting sends a notification to the spammer. Which is bad.
Send and receive invitations in Calendar on iPhone - Apple Support
I disable automatically processing those, as they tend to be spam. Log into iCloud.com, select Calendar, select settings (the gear), Preferences, Advanced, and select use email and not in-app.
This is what’s called “social engineering”, which is a fancy word for conning a sucker into doing something profitable. This happens a lot. Email scams, text message scams, phone scams, web browser pop-up scams, messages telling you about your recent Apple purchase of something; a purchase that never happened. Oh, and FWIW, email source addresses and phone call calling-number displays are easily forged...
Your iPhone or iPad device is very secure, assuming it’s running current software. What’s much less secure is the user of the device. Us. Which is why we’re all getting deluged with these scams, seeking to fool us, and to cause us to give over access ro our Apple IDs or other details. Or just to hand over all of our web browser and purchasing activities.
