In the last few weeks, I started having the same problem you described in your post about a year ago : new entries automatically generated in my Apple calendar app (iOS 26.5.2) without any title and assigned to a blue calendar that doesn’t exist.
Oddly enough, all I did was to go in the Calendars menu, uncheck all my iCloud calendars and then check them again and the bug disappeared. I didn’t think such a simple attempt would work but it did.
Since no solution was posted in your thread, I thought the community might be interested to know that this worked for me.