Do they still maintain it as in, it gets bug fixes and security patches? Technically yes, bug fixes and security patches are still produced for Windows Server. I wouldn't call it a good level of effort but it exists. They are happy to take your money for such a mediocre level of effort though.

Is it Microsoft happy path? No. Microsoft STRONGLY recommends that if you are running .Net (Core), you run under Kestrel on Linux in a container. Performance under Linux is much better than Windows.

Sharepoint, Exchange webmail, and other stuff uses it... that is why it's officially NOT depricated... but man imagine having to keep up an ASP codebase today, it's not unheard of, it's just rough.