The other option (vs full screen on additional monitor, potential issues on laptops with CPU and discrete GPUs) is to run PowerPoint in a windowed slide show. I have a 1440p monitor, and run PPT in a window a 1080+status bar pixels tall (ie. room to trim status area from window capture and not re-scale a 1080p stream/recording)
The beauty of this setup is that I can have the PPT window in the background, with a small portion always visible, bring the mouse over the PPT Windows Slide Show window, NOT make PPTx the Active Window, and still use mouse Scroll wheel to change slide
The challenge is NOT having a single 1080p monitor, running a 1080p stream, and wanting to capture the Slideshow. Window Capture works fine for that. The issue is controlling OBS Studio (typically in foreground) and then also interacting with (typically, just advancing) that slideshow. I've heard of folks using a PPT dedicated remote control pointer/stick/etc to manage PPT in the background. This would NOT be a typical general wireless remote that acts upon the foreground app