I can't switch back to Teams chat with Alt+Tab on Mac

Ok, I found a "solution" to force Teams to use the notifications. 

Simple version: 
01. You go to your teams https://teams.microsoft.com

02. When it asks for notifications, give the permission and that's it.

As an App in your dock:

02. You copy the URL from your logged-in teams-tab (01.)

03. You install Epichrome

(Very useful, you can wrap a Website as a App and it appears in the dock. Basically is MS doing the same with their "App" except it uses Electron, Epichrome uses Chrome or Brave.)

04. Start it, go through the wizard, when it asks for the URL, give your Teams-URL and a fine name for it.

(Icon can be automatically downloaded)

05. Start the new app, log in, give permission for notifications. Since it is basically a browser, it is forced to use the default MacOS Notifications. Alt-Tab works again.

Alternatively, there is a way to make a WebApp with chrome. But I never use chrome.