Yes, Bitter is hybrid ready HTML template. You can use it with Phonegap, Cordova or Webview for mobile apps or you can use it directly PWA apps.

You can buy it on themeforest.

Yes, Bitter using Bootstrap v4.4.1

No, Bitter is HTML, CSS, JS Template for Hybrid Apps which can be made by Phonegap, Cordova or Webview. You can use it for your PWA projects too.