Episode 22 was indeed the series finale of this show. However, two bonus episodes were produced, and FOX decided not to air them.
These episodes take place after most of the events in E22, but before the 4 years later time jump.
The episodes were converted to a standalone prequel movie, entitled Prison Break: The Final Break.
This is also known as produced episodes 23 & 24 of Season 4 (The Old Ball and Chain & Free).
