If you don’t receive calendar alerts on Mac
If you set an alert to occur before a calendar event but aren’t receiving the alert in Notification Center, there are several possible solutions.
Make sure alerts aren’t turned off in Calendar settings. In the Calendar app on your Mac, choose Calendar > Settings, click Alerts, then select “Show shared calendar messages in Notification Center” and “Show invitation messages in Notification Center.”
Make sure alerts aren’t turned off in Notifications settings. Choose Apple menu > System Settings, then click Notifications in the sidebar (you may need to scroll down). Go to App Notifications on the right, click Calendar, then select Banners or Alerts as the alert style.
Make sure a Focus isn’t active when you want to receive alerts. See Turn a Focus on or off.
Make sure event alert times are set correctly. Choose Calendar > Settings, click Alerts, then choose an alert time other than None for Events, All Day Events, or Birthdays.
Make sure you set up the alert properly. See Set alerts for an event.
If the alert is set to send an email, make sure your email address is correct in your card in Contacts. See Edit contact info.