"View by an Individual" = Windowed slide - which is what I use
One thing I noticed long ago when using Windows Capture (and OBS' older capture method so cursor not visible) is that if PPTx is NOT in slide show mode, then OBS window is not updated. So, have you tried putting PPTx in Slide Show mode? and is window still black at that point? If yes, make sure CPU isn't pegged at 100%, and if CPU ok, then look at Wiki regarding black screen on laptop (don't think you have multi-CPU, so probably doesn't apply, but just in case)
Also, it appears you are on a very old (for computationally demanding task of real-time video encoding) laptop. What are you doing for hardware resource utilization monitoring?
Having audio at 2 different sampling rates will most likely cause issues, especially on under-powered CPU. I recommend fixing that
To minimize workload on system, have base and output resolution be the same (no rescaling)
Using Chroma keying on such on old CPU... Uh, others will know more than I, but don't be surprised if you are asking too much of that CPU
