Allow apps to use your calendar information
Some apps and websites can use your calendar information to provide you with services and features. For example, an app might use your calendar to help you set up an event or a reminder. See Control access to your calendars.
To authorize an app or a website to use information from your calendar, click to allow access in the dialog. For some apps, you can give full access to all your calendars, or only allow events to be added your calendars. If you don’t want to authorize the use of your calendar information, click Don’t Allow.
If you allow third-party apps or websites to use your calendar information, any information they collect is governed by their terms and privacy policies. It’s recommended that you learn about the privacy practices of those parties.
You can review and change which apps and websites can use your calendar information in Privacy & Security settings.
Choose Apple menu > System Settings, click Privacy & Security in the sidebar, then click Calendars on the right. (You may need to scroll down.)