Re: Chrome shortcut
Yep, that's the main piece of it. Chrome will treat a site as installable when it finds a valid web app manifest, but there are a couple of other requirements before it offers the standalone experience consistently.
You'll generally want:
A valid manifest.json
A registered service worker
The site served over HTTPS
Appropriate icon sizes (192×192 and 512×512 are recommended these days)
Without the service worker Chrome may still let you create a shortcut, but it doesn't always launch in standalone mode depending on the browser version.
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