[Worker0] Tried select unknown importer

I see the error when accessing blender files that earlier could be autoconverted to fbx. In version 2021.2.11. These files that were not exported from blender but saved directly caused this error. Manually exporting to fbx stopped the error.

I had the same error when loading prefabs and prefab thumbnails. I tried this script for clearing the console every time the error pops out, but it worked only a few times and then the error started to appear again. Maybe it'll work for you. Place it to Scripts/Editor directory.

 using UnityEngine;
 using UnityEditor;
 using UnityEditor.SceneManagement;
 
 [InitializeOnLoad]
 public class ClearConsole
 {
     static ClearConsole()
     {
         PrefabStage.prefabStageOpened += PrefabStage_prefabStageOpened;
         PrefabStage.prefabSaving += PrefabStage_prefabSaving;
         PrefabStage.prefabSaved += PrefabStage_prefabSaving;
         PrefabStage.prefabStageDirtied += PrefabStage_prefabStageOpened;
         PrefabStage.prefabStageClosing += PrefabStage_prefabStageOpened;
         if(AssetPreview.IsLoadingAssetPreviews())
             Debug.ClearDeveloperConsole();
     }
 
     private static void PrefabStage_prefabSaving(GameObject obj)
     {
         Debug.ClearDeveloperConsole();
     }
 
     private static void PrefabStage_prefabStageOpened(PrefabStage prefabStage)
     {
         Debug.ClearDeveloperConsole();
     }
 }

With this problem always helps to update some packages in Unity->Window->Package Manager

I have same problem. In my case it's 2D project without any 3d objects.

Also experiencing this, I reimported the offending models as simple .obj files from Blender and it's still throwing this error.

If anyone reading is curious to try to reproduce this, grab the (free) model "Gold Coins" by Devtoid on the Asset Store. Those models all throw the error for me and I have no idea why.