Known service issue reported with Teams clients. There is a fix rolling out and should be complete by Monday. Here is the message for it, it has a few "work arounds" you can try, but not sure how much they really help.
"Title: Any user who is given control by a presenter during a Microsoft Teams meeting is unable to control the screen
User impact: Users who are given control by a presenter during a Microsoft Teams meeting are unable to control the screen.
More info: Depending on how impact is presenting itself for your organization, there are workarounds available. If no mouse or keyboard actions are working, users may click on one of the side rail items (such as Chat, Teams or Calendar) and then return to the meeting screen to mitigate impact. If a user has issues controlling the top of the screen, the sharer needs to move the shared app (such as a web browser or the Outlook client) down 40 pixels to mitigate the impact.
Current status: We've confirmed that the fix has been validated and has started to deploy to the affected environments. We're monitoring the fix to ensure it progresses successfully, and we suspect that the fix should complete by Monday, September 21, 2020.
Scope of impact: Your organization is affected by this event, and this issue could impact any of your users that are provided control by a presenter during a Microsoft Teams meeting.
Estimated time to resolve: Based on current deployment progress, we expect this problem to be resolved by Monday, September 21, 2020.
Root cause: A recent service update is preventing users who are given control by a presenter during a Microsoft Teams meeting from controlling the screen.
Next update by: Monday, September 21, 2020, 4:00 PM (9:00 PM UTC)"
