I'd like Notifications to work on Mac when I don't have the Teams app open. Maybe that Teams Helper app could run in the background as a daemon even when Teams.app isn't open.

I hacked it into working by making a second copy of the Teams app and adding <key>LSUIElement</key><true/> to the Info.plist file inside the package contents. Now I can always run the 'background' copy to get notifications with no dock icon and open the original Teams app when I want to use the interface.