I'm looking for a solution to generate an APK from Android App Bundle which will help me to share the App for internal testing rather publishing on Google Play Beta Testing.
Is there a way or a command using bundletool?
I think that the best option is to use Internal App Sharing that allows to test easily your App Bundles and APKs, including debug builds:
With internal app sharing, you can quickly share an app bundle or APK with your internal team and testers by uploading an APK or app bundle on the internal app sharing upload page.
If you want to go the bundletool route, you need to generate an universal apk. Take a look at this answer on how to do it.