If you’re not receiving calendar notifications on iCloud.com
If you’re not receiving notifications about events and shared calendars while signed in to iCloud.com or on your devices, you may need to change your iCloud Calendar settings.
Change iCloud Calendar settings
In Calendar on iCloud.com, tap the Action pop-up menu in the bottom-left corner, then choose Preferences.
In the Advanced pane, select “In-app notifications,” then tap Save.