Events in Calendar deleted after updating MacBook Air to Sequoia 15.0.1

My iPhone calendar is still ok but in my Mac book many of my events are deleted after updating to Sequoia 15.0.1

I cannot find any logic. In history and future, different calendars, created on phone and on mac, etc. Have to add them manually now to the mac calendar. Will cost me days to check and correct. Does anybody know what happened and how I can resolve?

[Re-Titled by Moderator]