No Annotate icons, whiteboard can't be shared

In my meetings, my clients have not got access to the Annotate button - it reportedly isn't present on their screen either on Windows 10 or iOS. I have added Whiteboards and created one in the last meeting, but the only two participants were me, 1 on PC with webcam, 1 on Android tablet.

How do I

1) Fix annotate so it shows and users can annotate my screen shares

And/or

2) Add participants to Whiteboard. I went through every option and setting (wasting meeting time) trying to find a way to add other users.