Google Mobile Ads Unity Plugin v6.1.1 won't load in Editor. Admob incompatible with Firebase?

I'm trying to make Google Mobile Ads Unity Plugin working, but it seems it is incompatible with Firebase already installed. How can I make those two work together?

1. When Mobile Ads plugin imported, I chose "I made a backup. Go ahead."

2. After automatic version dependency resolution I ended up with these errors: Assembly 'Assets/Firebase/Editor/Firebase.Editor.dll' will not be loaded due to errors: Unable to resolve reference 'Google.VersionHandlerImpl'. Is the assembly missing or incompatible with the current platform? Reference validation can be disabled in the Plugin Inspector. Unable to resolve reference 'Google.JarResolver'. Is the assembly missing or incompatible with the current platform? Reference validation can be disabled in the Plugin Inspector. Unable to resolve reference 'Google.IOSResolver'. Is the assembly missing or incompatible with the current platform? Reference validation can be disabled in the Plugin Inspector. Assembly 'Assets/Firebase/Editor/Firebase.Editor.dll' will not be loaded due to errors: Unable to resolve reference 'Google.JarResolver'. Is the assembly missing or incompatible with the current platform? Reference validation can be disabled in the Plugin Inspector. Unable to resolve reference 'Google.IOSResolver'. Is the assembly missing or incompatible with the current platform? Reference validation can be disabled in the Plugin Inspector. When I then go to Assets -> Google Mobile Ads -> Settings, I see only part of the inspector ui that I'm supposed to, only Google Mobile Ads App ID and AdMob-specific settings.

It doesn't show any AdMob options and when I fill in the Android App ID and restart the editor, it gets cleared.

I have the following plugins working in Unity Google Version Handler 1.2.166 Firebase Analytics (SDK 8.3.0) Google Play Games Plugin for Unity 0.10.12 Unity 2019.4.0f1 Any idea what might be the problem?