Open up your Microsoft Powerpoint slide, and from the top ribbon, click on "View" > Select "Reading View". Make sure that your powerpoint app is NOT minimized.
Open your Open Broadcaster Software (OBS), go to "Sources", click on "+" icon and choose "Window Capture". Give it a name and from the next popup's "Window" menu, choose the "powerpoint.exe" app. Once done, you will see the powerpoint slide in the preview area.
