PWA Any Website with a bookmarklet on iOS/Android

youtube_pwa.js

javascript:(function() {
    var manifestContent = {
        "name": "YouTube PWA",
        "short_name": "YouTube PWA",
        "start_url": "/",
        "display": "fullscreen",
        "background_color": "#000000",
        "theme_color": "#FF0000",
        "orientation": "landscape-primary",
    };
    
    var dataUrl = 'data:application/manifest+json,' + encodeURIComponent(JSON.stringify(manifestContent));
    
    var link = document.createElement('link');
    link.rel = 'manifest';
    link.href = dataUrl;
    document.head.appendChild(link);
    
    alert('Custom manifest.json has been inserted!');
})();

This bookmarklet generates an inline manifest.json file for youtube specifically but can be applied to literally any website a user may want to create a custom manifest file for.

The major benefit is that you can have fullscreen apps for websites that otherwise would not allow you to create a fullscreen app/experience for.