In system preferences > iCloud if you uncheck the box of calendar the calendar syncing will stop , once again check the box for calendar the calendar will start syncing ( noticed over the calendar application a bar loaded very fast stating uploaded calendar to server account and vanished ) .
It depends what way have you signed in with Apple ID , if Apple ID address and password is same as gmail address , and in system preferences > iCloud the Apple ID is signed in and calendar box is always checked the syncing is activated and whatever events you had created in the server account ( it could be with gmail server or in the iCloud server ) they will always be inevitably there , you must have not crossed the designated iCloud storage space it could be free 5GB or you had purchased a storage plan .
The excessive data that was used through calendar from the iCloud server won't stay , only the data that is within limits will again sync .
Its not a rule that only calendar occupied most of the space , some other application might also have consumed the data like photos , notes , mails , iCloud back up ..

You can reduce the iCloud storage space see some articles https://support.apple.com/kb/PH12790?locale=en_US
https://support.apple.com/en-gb/guide/system-information/sysp4ee93ca4/mac
https://support.apple.com/en-in/HT206996