safari browser slows down significantly because of calendar - MacBook air 2017/Monterey -

MacBook air 2017/Monterey -

After getting a checkup/tuneup and new battery the guys at the computer store said that calendar in my laptop is using a large portion of energy, and is the cause of significant slow-down when using safari, specifically.

What can I do to clean stuff/data from the calendars on my laptop, (dating back 10 or so years)? Each time I purchased a new computer I guess all that was migrated.

Thank you