We just upgraded to 16.12.0.0 from a really old version.
And now users with Mac get the initial zoom of 10% on ppt files and 66% on pptx files. This has never been an issue before, and we have never set any zoom our selves in the files generated. This has just worked fine before.
I have attached two slides and a screenshot of how a ppt file opens (which had to be censored a bit, but you will get the picture).
I have verified the generated presentations in PowerPoint 2010 and PowerPoint 2013. However, I have only been able to reproduce the issue in PowerPoint 2010. I have also observed that you are using Aspose.Slides for .NET 16.12.0 on your end. The latest version available at present is Aspose.Slides for .NET 17.2.0 and I suggest you to please first try using the latest version on your end. If you are still able to reproduce the issue then please share the working sample project along with source presentation so that we may investigate the issue further.
I have worked with the presentation file shared by you using Aspose.Slides for .NET 17.2.0 and have been able to observe the issue. An issue with ID SLIDESNET-38526 has been created in our issue tracking system to further investigate and resolve the issue. This thread has been linked with the issue so that you may be automatically notified once the issue will be fixed.