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.

Unfortunately sibling petitions are among the longest family based immigration processes. Depending on the country of birth, the wait can easily be more than a decade. The best way to monitor progress is by checking the visa bulletin each month and comparing the priority date on the approval notice.