How to fix PowerPoint "cannot read" error?

Are you trying to open the file by doubling the file icon? If so, try launching PowerPoint and then use its "File > Open..." menu command. If that fails...

MS Office/PowerPoint is not an Apple product and there are not as many Office users active here as one would think.  MS Office questions posted in Apple’s forums can linger here a long time without getting effective help.

I believe you will be better and faster served by asking in Microsoft's Office forums.

https://answers.microsoft.com/en-us/msoffice

Be sure to include "mac" in your search string to limit the search to Outlook Mac topics. Similarly, if you post a question include "Mac" in the title. That makes it easier for other Mac users to search for new posts.

I believe you will find the contributors there knowledgeable and very helpful, much more so than MS's hard-to-use, Windows-centric support documents.

PowerPoint is a Microsoft product, correct?

Contact a third-party vendor - Apple Support

If you are attempting to open it with Microsoft PowerPoint and it won't open, try opening it with Keynote.

Keynote - Apple