I am experiencing the same issue. Only only occured when I upgraded my project to use the latest Firebase SDK in order to support the new Target API Level.
This is a minimal example of a project with this issue.
Firebase Unity SDK Version 12.2.1
Unity editor version 2022.3.45f1
Installation Method .unitypackage
Problematic Firebase Component(s) Auth
Targeted Platform(s) Android
Unity editor platform Ubuntu 20.04
Scripting Runtime IL2CPP
Release Distribution Type Pre-built SDK from https://firebase.google.com/download/unity
git clone https://github.com/grantwwoodford/FirebaseSample.git
cd FirebaseSample/
git lfs pull
Open "Assets/Firebase/Sample/Auth/MainScene.unity"
DllNotFoundException: FirebaseCppApp-12_2_1 assembly: type: member:(null) Firebase.AppUtilPINVOKE+SWIGExceptionHelper..cctor () (at /home/runner/work/firebase-unity-sdk/firebase-unity-sdk/linux_unity/app/swig/Firebase.App_fixed.cs:3958) Rethrow as TypeInitializationException: The type initializer for 'SWIGExceptionHelper' threw an exception. Firebase.AppUtilPINVOKE..cctor () (at /home/runner/work/firebase-unity-sdk/firebase-unity-sdk/linux_unity/app/swig/Firebase.App_fixed.cs:3978) Rethrow as TypeInitializationException: The type initializer for 'Firebase.AppUtilPINVOKE' threw an exception. Firebase.AppUtil.SetLogFunction (Firebase.LogUtil+LogMessageDelegate arg0) (at /home/runner/work/firebase-unity-sdk/firebase-unity-sdk/linux_unity/app/swig/Firebase.App_fixed.cs:4688) Firebase.LogUtil..ctor () (at /home/runner/work/firebase-unity-sdk/firebase-unity-sdk/app/src/LogUtil.cs:81) Firebase.LogUtil..cctor () (at /home/runner/work/firebase-unity-sdk/firebase-unity-sdk/app/src/LogUtil.cs:37) Rethrow as TypeInitializationException: The type initializer for 'Firebase.LogUtil' threw an exception. Firebase.FirebaseApp..cctor () (at /home/runner/work/firebase-unity-sdk/firebase-unity-sdk/linux_unity/app/swig/Firebase.App_fixed.cs:1924) Rethrow as TypeInitializationException: The type initializer for 'Firebase.FirebaseApp' threw an exception. FirebaseManager.CreateFirebaseApp () (at Assets/Firebase/Sample/Auth/UIHandler.cs:32) FirebaseManager.Start () (at Assets/Firebase/Sample/Auth/UIHandler.cs:24)