Please give the following information:
- The version of your PowerPoint.
You can check it via PowerPoint menu>About Microsoft PowerPoint.
- The screenshot of error message.
- Does this issue occur when opening the same files on another Mac that has different operating system?
- Does this issue occur when using other Office applications?
After checking the information above, I suggest you to update Office.
If it doesn’t work, please uninstall Office completely and then reinstall it.
Besides, you may also try rebooting Mac in safe mode, this helps you check if this issue is caused by incompatible login items or others.
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