Hi there,
You can get the received date from the email, which in your case would be the sent date as it is coming from your sent folder.
Instead of trying to insert the date directly into the 'Create Event' action where the property is not available, you first need to pull the 'Received Time' property into a variable. This will then become available to your action and will work as required after formatting the date correctly (using the 'FormatDateTime' expression).

Expression for the 'Start Time' field (which contains to the 'EmailCreated' variable created earlier in the flow):
formatDateTime(variables('EmailCreated'))