Hi @Andrew Paine,
Unfortunately, looping a PowerPoint presentation directly in SharePoint is not supported by Microsoft. However, there is a workaround that you can try. You can convert your PowerPoint presentation to a video format that supports looping, such as MP4, and then upload it to Microsoft Stream, OneDrive for work or school, or SharePoint. From there, you can embed the video in SharePoint and set it to loop.
To convert your PowerPoint presentation to a video, you can follow the steps in this article: Turn your presentation into a video. Once you have the video file, you can upload it to Microsoft Stream or SharePoint, and then embed it in SharePoint.
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