For work I use an Exchange account that I configured on two iOS devices, two iPads and two macs.
Only on iOS and iPadOS I see old repeating events dating back to the years 2005-2010.
These events are no more present in my calendar (I can check with the Mac, Outlook or even with the Exchange web interface). They only appear striped on iOS.
If I click on the event all the options to accept or decline are not present.
I never delete emails so it could be that the original invitation is present in the Archive folder.
I remember an option to automatically add events found in email, but I don't find it in the calendar or mail settings.