Other methods of installation

This step isn't required. This is if, for example, BundleTool doesn't work, or that you used the AAB -> Universal APK.

When AAB -> Universal APK used

This method gave you a .apk file, that you can just open in Android, or use adb install Path/To/Apk.apk to install from the computer.

Other ways for APKs

You can use, in Android, for example, File Manager + (On F-Droid and Google Play Store), which provide support for .apks (simply clicking on it will install the app). It doesn't seem that the Native File Explorer support .apks, so it is a File Manager + functionnality.