Expo runs as a set of small always on top windows. A launcher, a dock, a response panel and the notes view. Each one can appear over a video call, which means each one can ruin a video call.
The rule we settled on is that no Expo window ever takes focus unless you clicked it. That sounds obvious and it is surprisingly involved once you add multiple displays, full screen apps and a machine waking from sleep.
The dock also had to survive the worst case, which is a display being unplugged mid call. Bounds get clamped to whatever screen is still there rather than the window quietly moving off the visible area.
None of this shows up in a feature list. It is the difference between an overlay people keep on screen and one they close after the second call.