Microsoft Test Manager? Isn’t that a cloud product?
No, not really. Microsoft Test Manager actually refers to the on-premises application that is used to test desktop apps.
The naming is a bit unfortunate here.
Azure Test Plans used to be called “Test Manager” up until recently and is indeed a cloud product. I suspect that part of the reason for the rename was the fact that there was a lot of confusion between the two.
What’s happening with the client application?
Microsoft recently published documentation around this. As you can see Microsoft Test Manager will be supported until 2020 in Azure DevOps (cloud) and up until Azure DevOps Server 2019 goes out of support on-premises.
You will also notice that it is no longer included along with Visual Studio 2019.
Is there a replacement when it comes to testing desktop apps?
There isn’t a direct replacement, but Azure Test Plans now has a desktop test runner, which can be downloaded directly from Azure Test Plans. (both on-premises and in the cloud)
For many manual testing requirements, you may be okay just using the Test & Feedback extension which works in Chrome, Firefox, and will be supported in Edge Chromium once it becomes generally available.