So I did a test run of my presentation. It worked very well, except that the YouTube videos I had embedded were playing but the tester couldn't hear the audio from the videos.
Turns out it was a simple solution: you have to click "share computer audio." Who knew?
I have to say, everyone is on a learning curve with COVID. We're all trying. And that is what amazes me so much about the Kritzerland presentations. Complicated stuff, done so seamlessly. I was going to say "effortlessly," but I know that there has to be so much hard work going on behind the scenes.