I have tried creating a VSTS tab that links to our overview dashboard in DevOps (formerly Visual Studio Team services) but the page simple states 404 not found (see the attached diagram). The 'Go Back Home' link on the error page takes us back to the root of DevOps.
I suspect this problem has been caused by us upgrading our VSTS/DevOps organization to use the new DevOps url path (as recommended by Microsoft), as we've seem another issue along these lines when adding a VSTS profile to GitKraken. The paths are as follows:
Please note this is different to the other issue we see with VSTS tabs in Teams, where the desktop version shows a blank page instead of our dashboard but the web version of Teams does not (when using the old VSTS path).