Hello everyone and thank you for taking the time to request this feature. As part of our investigation on adding this capability, we ask that you please help us gather additional information on how you use Pin. This helps us to prioritize and design the feature to be exactly what you need to get more done!
Please use the below link to access a short survey about Pin:Tim commented
If you flag an email on the desktop version, you can then go to "View Settings" in he "View" tab choose the "Sort" function and have the first priority be given to flagged items. Under "Then by" chose "Received". This will automatically list all flagged emails first followed by date.