OS-Native Teams Notifications can be enabled even if your organization disabled beta access, by modifying the settings request with a proxy software such as Charles or Proxyman.
I found the following instructions on the macOS UserVoice ticket mentioned above:
Instructions:
- Install and open Proxyman
- Select "certificate > install certificate on this mac" from the menu and follow the steps
- enable https response for teams.microsoft.com
- option-click on teams.microsoft.com > tools > scripting
- create new script for
https://teams.microsoft.com/package/desktopclient/settings/osx with the following onResponse function:
function onResponse(context, url, request, response) {
// Update Body
var body = response.body;
body["settings"]["enableNativeNotification"] = true;
body["settings"]["enableMacNativeNotification"] = true;
response.body = body;
// Done
return response;
}