bundletool utility is mainly used to generate APKS sets and not APK files, however it should be still possible to export to universal APK archive.
This can be done with the following command:
bundletool build-apks --mode=universal --bundle=/MyApp/my_app.aab --output=/MyApp/my_app.apks
It will also generate .apks file but inside the container there will be just single .apk file.