You can definitely add a PowerPoint presentation to ExpandShare, either by uploading the file in the Library or using as part of a Course or Learning Track.
Consider the content and the audience first. If the PPTX presentation is something that your users will need to open and edit in Microsoft PowerPoint in order to use, then it makes sense to share the native file format. Post in the Library and users can download it to their devices for editing and playback.
However, if you just want your audience to view content that just happens to be in the format of PowerPoint slides, consider if all of your users will have Microsoft Office for iOS/Android installed on their mobile devices. If not, they will not be able to open the training. This is more typical, so we recommend converting PPTX slide decks into something easier to consume by mobile app users.
Three good options are exporting the slides to a single PDF, individual images, or as video with audio/voice over. PDF is the best solution if you are posting the presentation in the Library for viewing but not editing. This preserves the formatting and pagination, and every word in the presentation will also be search indexed, making it easier to find.
If you want users to consume your presentation slides as part of a Course, we recommend that you either save each slide as an image (PNG or JPG) or convert the PPTX deck into a video, ideally including voice over audio.
Once your content is in video format, it's easy to upload into a Course and easy for users to view on any device. I've included 2 links to external instructions explaining how to do this:
PowerPoint 2021/2019/2016/Microsoft 365: https://support.office.com/en-us/article/turn-your-presentation-into-a-video-c140551f-cb37-4818-b5d4-3e30815c3e83
PowerPoint 2010/2013: https://24slides.com/presentbetter/tutorial-save-your-powerpoint-as-a-video/
You also can include any Library document, such as a native PPTX file, PDF export of a PowerPoint, Image saved from a PowerPoint deck, or movie of a presentation deck, as part of a Learning Track. Check out https://expandshare.freshdesk.com/solution/articles/43000036539-how-to-create-learning-tracks for an explanation of how to build and assign Learning Tracks.