You're seeing a static preview of this file, so the buttons won't work. To actually run it:
iPhone: tapping the file only ever shows this dead preview.
Open it in an app that runs HTML — a free code-editor/HTML-viewer from the App Store — or open the
shared link in Safari.
Android: in Files, press-and-hold the file → Open with → Chrome
(not "HTML Viewer").
Computer: just double-click it — it opens in your browser and works.