I am a US citizen and I filed a petition for my brother who lives overseas about 6 years ago. I have not heard anything since then except the original approval notice. Is this normal and how long does it usually take

Family petitions for siblings of US citizens fall into a category that often has very long waiting periods because of annual visa limits. It is normal for these cases to take many years before a visa number becomes available. The approved petition simply holds a place in line until the priority date becomes current.