This Repo will explain how you can control admob banner in your flutter application.
Demo. In this demo you can see, when you click on show banner ad it will display Banner ad and when you click on hide banner ad, it will dispose the banner ad.
You will need only one plugin firebase_admob: ^0.5.2
Yes, you can clone this Repo and check how it works.
I am not sure, it really depends on gradle version you are using as well as flutter version.
Here is my Flutter Doctor details
[√] Flutter (Channel stable, v1.12.13+hotfix.5, on Microsoft Windows [Version 10.0.18362.356], locale en-US)
[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
[√] Android Studio (version 3.5)
[√] VS Code, 64-bit edition (version 1.41.1)
[√] Connected device (1 available)
• No issues found!