The best I've seen is (verbatim) "Excellent Javascript(ES6) and CSS skills with minimum 10 years of Java (enterprise) for services/apis development experience, 5 years experience in ReactJS/redux or similar, 5 years nodejs"

I've found that the understood meaning of .NET has changed from when the term was first defined by Microsoft. Originally it meant the C# language and the multi-language library that it employed. Now it means specifically the parts of that library that are used for server applications.

Eh, I hear people talk about .NET desktop apps all the time and they are understood quite well. .NET (and, frankly, everything that isn't HTML/CSS/JS) may be less used outside of backend use than was once the case, but I don't think .NET is conventionally understood to be backend-specific in any general sense.

Perhaps that's still true in casual conversation, but in the hiring world .NET appears to be about server applications exclusively. At least in my observations.

Yeah when I see anything .NET related, it's always backend or fullstack oriented positions.