Use the Accessibility Checker as you create or edit a PowerPoint. Click Review - Check Accessibility to use the checker.
As you make your PowerPoint, think about how you will post it in Canvas. You have 3 options:
"Closed captions, subtitles, and alternative audio tracks are not preserved when you use the Compress Media or Optimize Media Compatibility features. Also, when turning your presentation into a video, closed captions, subtitles, or alternative audio tracks in the embedded videos are not included in the video that is saved."
"One simple step towards inclusivity is having a unique, descriptive title on each slide, even if it isn't visible. A person with a visual disability that uses a screen reader relies on the slide titles to know which slide is which. You can position a title off the slide. That way, the slide has a title for accessibility, but you save space on the slide for other content. For instructions, go to Title a slide and expand the "Put a title on a slide, but make the title invisible" section." - quoted from the Microsoft web page, Make your PowerPoint presentations accessible to people with disabilities.
Watch this 2-minute video from Microsoft to understand why this is important and see how you can make sure the items in your slides are read by screen readers in the correct order.