Add an exception for makemkv.exe or makemkvcon.exe .
Standard official firmware on 4K drives often blocks the reading of encrypted sectors entirely. If your drive isn't "friendly" or flashed with decrypted firmware, no amount of key downloading will fix the issue. You can check your drive status in the right-hand information panel of MakeMKV; it should say makemkv automatic hk downloading is disabled or failed
If step 2 fails, you see: "Automatic HK downloading is disabled or failed." Add an exception for makemkv