Hi Sadie,
Thank you for posting your question in this community. Based on your description and screenshot, the problem could be related to your Adobe Acrobat.
First of all, I am not sure which PowerPoint for Mac version you are currently using. If it is not the a latest version, I suggest you can update it to the latest version first for the starter. In addition, you can check PowerPoint for Mac version by clicking on PowerPoint menu > About PowerPoint to find details and share a version with us at your convenience.
For your information:
Update history for Office for Mac
In addition. Did you try to remove Acrobat add-in file from Library folder. Here are some similar threads about this issue. I suggest you can also try out the methods in the following threads to remove Acrobat add-in file in Startup.localized/PowerPoint.
For your information:
New Error: "Run-time error '53'" ... MacPDFM Reply by John
Run-time error '53' Reply by John and Clark
Best regards,
Dihao