Same issue others have described. As soon as Mac PowerPoint updated to 16.13, Delete and Arrow keys stopped working. These keys work fine in same versions of Excel and Word. Closing/opening PowerPoint and rebooting do not solve.

Contacted MS support chat yesterday. One ended the session as soon as read my description of the problem. Another referred me to call the toll-free support number and speak with a PowerPoint "expert". After 10 min on hold I opted for callback which is yet to come 24hrs later. Not impressed.

Seems like the only way to solve is either wait for MS to issue another update or, better yet, downgrade to prior version if possible.