After a microflow finishes, an instruction set is send back to the client (browser). This set includes instructions like “show pop-up”, “close page”, “refresh these objects”, “navigate to page”. The exact timing of the progress bar being hidden and these instructions cannot be influenced using a microflow. All instructions are being executed first, before the progress bar is hidden.
Don't forget to add error handling like shown below, otherwise your users are stuck with a progress bar which will never disappear.
Hopefully this helps!