Depends
Are you talking about having PPT in a full screen landscape slide view? or something else?
When I first started a year plus ago, I only had a single monitor. I made that a large monitor in high resolution, and then put PPTx into a Windowed slide show, then did a window capture (with PPT window manually sized to be desired resolution to not rescaling). Then I could control OBS, and with only a portion of the PPTx window visible, a mouse over (without making PPT active window, I could advance slides which worked for me)
So your issue is likely to be what are open active windows, and how are signals sent to various apps. You could probably use a remote pointer/clicker that can be configured to ONLY talk to PPTx (do your homework, most pointers only talk to OS and assume PPT is full screen)
There are plugins for sending commands from OBS to PPT (though a challenge with more recent Office/PPT security paradigms since becoming Office 365). You can also put macros in the PPTx and use that via websockets to control OBS
so... depends on what you are trying to accomplish.
Adding a 2nd monitor (even if a small one to a laptop) is usually much easier