Thanks for the reply - You hit the nail on the head. I have not figured out, though I've heard it mentioned several times, that there is a way to tie an audio input source to a scene. Seems when I create an audio source, it shows in the mixer and is just there for all scenes. If I mute it, it is muted for all scenes. In some scenes I need the mic on. Thats why I was looking for some automated way to mute it for a particular scene. I may have missed something somewhere if it can actually be done. I'm running OBS 25.0.7 on a MacBook Pro / Catalina. If there is a way to tie a mic to a scene, let me know.
As to PowerPoint, we use a program on a separate computer called Song Show Plus (but could be any program including PPT) which uses its own picture format for bible verses and song lyrics but can display PPTx files as well. I installed NDI tools from NewTek and load NDI Scan Converter on the SSP machine (Windows 10). You can create a Scene with an NDI source in OBS, specify the source as a particular machine, a particular monitor if there is more then one on that machine, or just a section of the screen. It will pull the image of the slide show over the local network. No measurable delay so if you are constantly updating slides for song lyrics for instance, you only need one scene since it updates the slides to OBS with no noticable delay.
All the best,
Bob