In Teams when in video chat with only 1 other person and click Share Content | (there is no Whiteboard app)
When I add someone else to the call I can see the whiteboard app.
This is weird and wastes a lot of time debugging why this feature comes and goes. The button should always be there and if Microsoft don’t want to enable it for 2 people for some reason pop a message that says “Whiteboard is for 3 or more users”.