I installed the latest FMOD 2.3.15 in an empty Unity 6.6 project and got this error.
[Worker1] UnityException: Calls to “AssetDatabase.AddObjectToAsset_Obj” are restricted during asset importing. AssetDatabase.AddObjectToAsset() was called as part of running an import in a worker process.
UnityEditor.AssetDatabase.AddObjectToAsset_Obj (UnityEngine.Object newAsset, UnityEngine.Object sameAssetFile) (at :0)
UnityEditor.AssetDatabase.AddObjectToAsset (UnityEngine.Object objectToAdd, UnityEngine.Object assetObject) (at :0)
FMODUnity.EditorSettings.AddPlatformToAsset (FMODUnity.Platform platform) (at ./Library/PackageCache/com.fmod.fmod-for-unity.v203@4f71248df90c/FMOD/src/Editor/EditorSettings.cs:705)
System.Collections.Generic.List1[T].ForEach (System.Action1[T] action) (at :0)
FMODUnity.EditorSettings.AddPlatformsToAsset () (at ./Library/PackageCache/com.fmod.fmod-for-unity.v203@4f71248df90c/FMOD/src/Editor/EditorSettings.cs:697)
FMODUnity.Settings.OnEnable () (at ./Library/PackageCache/com.fmod.fmod-for-unity.v203@4f71248df90c/FMOD/src/Settings.cs:650)
UnityEditor.AssetImporters.ScriptedImporter:GenerateAssetData(AssetImportContext)