In my brief testing just now, both extensions seem to be purely synonyms. Microsoft's documentation suggests that .razor is for Blazor components and .cshtml is for Pages, but even Microsoft's own templates are inconsistent on this and seem to use them interchangeably. The view engine doesn't seem to care what you call it and doesn't really seem to change its behavior. It really mostly just seems to underscore the difference between Razor Pages and Blazor "Server-Side Only" is real blurry to nonexistent. Obviously Blazor Hybrid and Blazor WASM have very different behavior from just Razor Pages.