Add new Google Calendar events to Notion and then post to Slack -

If

New event added

This Trigger fires every time a new event is added to your Google Calendar. Note: The time in the ingredient will be based on the timezone set in Google Calendar.

Then

Add item to a To-Do list

This action will add a to-do item to an existing Notion To-Do List template.

And

Post to channel

This Action will post a message to the channel you choose in Slack.