Why can't localhost see index.html?

Question

Android

I am making a Spring REST application according to the video tutorial , the author creates an index.html file and enters a couple of lines there. I write the same thing, but my localhost does not see my index.html at all. And I had to manually specify the file type (because I do not have .html in the context menu as the author) and manually enter the code from the template. And two questions arose: why, in fact, the same actions do not give any result for me, and is it possible to put .html in the context menu for creating a file?