I had this exact this happen to me this evening. It’s a scam trying to get you to click the link in the description. I found that the internet (inc AI) suggestest finding a rogue calendar and deleting. My issues was the appointments where part of my hotmail calendar! When I logged in online (separate device) the scam appointments were not there!
what worked for me was to go to setting>calendar>accounts select the account that has the false appointments on (hotmail for me) and the turn calendar sync off. It will say all calendars will be deleted from the device but that’s ok because the data is stored on hotmail server. Once the calendar was clear I when back and clicked the “sync” calendars again. Every event from my real calendar came back but not the false ones. I don’t know how they did it but I now have a usable calendar. I’m just glade that I have two factor security enabled or I would have worried that my account might have had to have ben scrapped.
Hope this helps.