I finally figured out how to make presentations full screen on the Mac.
I'm using Chrome to display the presentation.
In Chrome's View menu turn off the first three options.
Choose Enter full screen.
Voila — full screen!
Whew.
BTW, neither Claude.ai or ChatGPT knew that Chrome has all the functionality needed to do this. The commands were in the same menu as the one command the both insisted would do it. So this human beat them both on something they really should’ve been much better at.