Whiteboard: “Disable annotation" feature missing

I teach kids who need to be able to scroll without writing on the Whiteboard. I also need to be able to turn on and off their ability to write on the whiteboard. After using this feature in my online classroom for a while, it now appears to be missing.

As I recall, in the past I’ve been able to simply turn off the ability for a child to write on the whiteboard: easily found and easily done. Help files direct me to the three dots (More) dropdown menu, where “disable annotation” should be one of the options. However, my “More” dropdown does not include “disable annotation.” I’ve searched every menu and control I can find without success. This feature is absolutely necessary for my daily work.