I have the very same issue: no option to “Livestream to Facebook” when I open a recurrent meeting from the Zoom app on iPhone. But I am able to see the option to livestream to Facebook from the Zoom app client on my Windows laptop.
I have same exact issue and I did go out and come back in. I wonder if it's not a possibility on Mac? I also tried through my Android phone and at least the Youtube option came up but still no FB.