Additional features, settings, or issues not covered by specific Microsoft Teams categories
I kind of found a workaround that seems to working for me but I had to switch to the teams web app.
Open the DevTools (Chrome) and switch to the Network tab. There you can see alk the network requests Teams does.
Now select the request "https://presence.teams.microsoft.com/v1/me/reportmyactivity/", right-click on it and select block url.
Minimize DevTools window (keep it open).
Done.
I know it is ugly :)
Another solution would be to use something like pi-hole.net and block the url there. This should work for the Desktop version too but it can be more difficult to setup for some people (or even imposible depending on your environment).