Aside: I don't understand the premise of this thread that suggests it's a "SPA" just to, say, use React on a single page of an application. The whole basis of the "SP" in "SPA" is that the Javascript (state) spans multiple pages.
ASP.NET Webforms? I have good memories of being able to do that easily, with zero (or almost zero) JavaScript.
It's not the best user experience ever (the whole page has to reload after each click, and the state is persisted by serializing structs in <input type="hidden"> fields), but I had a pleasant experience when I developed with it.
ASP.NET Webforms components were the best thing until we finally had React/Vue!
The only problem was that it was way too easy to make a mess in your backend code.