Don't show notifications if the window is visible
Notifications are really not needed when the Teams window is visible, it should be possible at least to disable them. I find them esp. noxious and attention-grabbing when looking up information while I'm chatting with someone. Chances are I'm already aware that the person replied, I don't need a reminder of that.
To avoid missed messages because the window was not actually visible or not looked at, an option would be to have a (configurable) 5-minutes recap: "Bob is waiting for your reply" or "The XX channel has been quite buisy".