To auto play a PowerPoint file when you click on it. First save the file as a PowerPoint Show files “PPS”. Then when you click on the file, it will automatically play in slideshow mode.
Make sure you don’t select “PPT” which is a regular PowerPoint file.
See:
https://www.presentationmagazine.com/automatically-open-ppt-attachment-in-slideshow-mode-18146.htm