Thank you for writing to us. Photoshop Mix does not have an option to save in reduced file size. Please help us understand your workflow for the same. Thanks.
This is one of many problems with Adobe products now. A simple file size cannot be changed in PS Mix. You can’t crop in Draw. To change colors in Mix you use layers & no fill. PS Touch did all of this. No jumping from app to app to work on a project. That is why I canceled the subscription to CC.
Another problem with too too many apps is that some of the Adobe employees don’t even know how they all work. I‘ve seen responses “try using Draw or Fix” rather than explaining to the person how it can be done.