Power Automate’s Bookings connector only works with shared booking pages, not personal ones like Book with Me. That’s why you’re getting the “Bookings mailbox not found” error.
Use the Outlook calendar trigger “When a new event is created and select the Calendar where the Booking meetings land. In the trigger conditions you can filter based on the Subject/Title of the event to only filter out the personal bookings.
@equals(triggerOutputs()?['body/subject'], '<Booking event name>')
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