Do truly air-sealed electrically-actuated duct damper exist?
Truly air-sealed electrically-actuated duct dampers exist.
What you are asking for is also known as a electrically actuated butterfly valve for air.



They can be found at industrial supply stores such as Mcmaster Carr, and a makeup air duct sized one will cost around $600-$2000

If you are in a DIY mood you can probably get one of the cheaper manual ones around $200 and retrofit your existing duct damper motor to it