What can prevent the PowerPoint executable from closing via task manager?

Could you explain a bit more? You tried to end the task and what happened? Any message? Nothing?

There was no messages when I tried to end the task; task manager said not responding. The only way to utilize Power Point again was to restart the system.  The other way to utilize PowerPoint after it stopped responding was to  log out the current user. Note, PowerPoint I believe was still  hanging when I logged out the current user, the reason I say this is because I executed an online repair of Office 365 and it told me that an application is opened.

This lead me to believe that something is utilizing the executable and it would not release control of it, it is something that does not respond to administrative rights: for instance, when I open task manager with admin rights and try to close PowerPoint, it does not work.

But the good new, I can open an new instance of PowerPoint, when one is hang.

It look like I will have got scan fo undesirable software in SafeMode, using Windows Defender.

Not sure if this helps but Windows File Explorer will create an invisible instance of PowerPoint if the user clicks on a PowerPoint file in Explorer when the Preview pane is active.