Yikes all 3 of the entries (9, 10 & 11pm) would freak me out too... And I bet all 3 hv different links, each taking you to malware ****!
U said you aren’t aware of having gotten unsolicited invites, but “add event to calendar“ could so easily be clicked in any email or on any webpage... inadvertently by accident... That is likely how it got there.
If you could hold down those links on your calendar without opening them, so that you’re offered the option to copy the URLs, that’s what I would do. You could then paste them into notes or something else to check safely. You definitely want to delete that whole day of events from your calendar if possible. .
Never saw such a thing but bad actors are sure creative these days!
I will follow your inquiry in hopes of you sharing what you might discover.
Good luck