Tools for the file, not just the form
Most converter sites offer an icon resizer and a package-name generator. The problems people actually hit when turning HTML into an APK are earlier and later than that: the file itself is not ready to be bundled (a CDN script, a module import, a path that starts with /), and after the build Google Play asks for a signing key, a privacy policy and a Data safety form that a builder cannot fill in for you. These tools cover that stretch — from a blank index.html to a listing that passes review.
None of them uploads anything. Files are read with the browser's FileReader, images are drawn on a canvas, scans are pattern matches on the text you paste, and every download is generated locally. They work offline once the page has loaded.
When the file is ready, the builder takes it — a single HTML file or a ZIP of a folder — and returns a signed Android app in a few minutes.