Hello Charlie, and thanks for reaching out to us via the forum!
Have you tried creating an Area Integral result control item at the outlet? This should help you monitor the flow rate at the outlet, but this item must be created prior to the simulation run to be available in the results.
Another alternative is to use the Statistics option in the post-processor. Ensure that you are visualizing the Velocity values in the Parts Color filter. Clicking on the outlet face with the Statistics option should give you the flow rate value as follows:
Let me know if you need further assistance!
Best regards, Kaan