Microsoft Teams does not have a “true” fullscreen mode. Even if you select both “focus” and “fullscreen” there is always a command bar left at the top. This can make it difficult read small text when people are sharing their (high resolution) screens. Here are two tips how to improve:
1. Pressing Ctrl+Minus will make the Teams GUI smaller. Do this multiple time. Each time the shared video gets more room! (You can always press Ctrl+Equals to go back to 100% zoom.)
2. While hovering the shared content, hold Ctrl and use the mouse wheel to zoom in and out. Only the shared screen is affected. When zoomed in, use the mouse to drag the content around.
3. Use the web version of Teams instead. This actually has a *real* fullscreen mode. (It’s not a problem to have both the web version and the ordinary desktop client running at the same time!)
As a side note: From time to time I’ve had problems with viewing screen shares in Teams. The framerate of the incoming video is extremely bad and drops to something like one frame per *minute*. In these cases I have had better result using the web version instead of the ordinary client. Still not super fluid, but at least good enough so you can follow the conversion.