Activate iCloud but keep calendar private My company invited me to join its iCloud calendar.

On my iPhone I didn't activate "Calendar" in the iCloud settings until now for data privacy reasons.

Will my private calendar on my iPhone be synced to my personal iCloud as soon as I activate the "Calendar" switch in the iCloud settings? Or does my private local calendar stay local and I'd need to transfer my local calendar to iCloud manually if desired?
iCloud will automatically sync all calendars not located on another server (such as a Google Calendar). It will take a few minutes to sync all the info to iCloud, then it will be available across all devices. Nothing stays local when iCloud is involved. It goes to the cloud, and syncs when it detects changes.