Additional meeting and call-related features and issues within Microsoft Teams for business
White Board is not a bad temporary work around, but it is not a solution to this issue. Probably the only feature that gives Slack an edge over Teams.
Why do you need this... when the person is sharing screen you want to quickly communicate a change. the lack of this feature is slowing down productivity 10 fold and I am suggesting my company reverts back to Slack because of it. Seeing the large number of complaints is telling me two things, you are aware of the issue and you are not making an effort to resolve