Upvote:3
An I-20 is not a visa. So yes, you need a transit visa for Germany if your US visa has already expired.
Per Timatic https://www.timaticweb2.com/integration/external?ref=d975cfc59f5c0abd06d16e872198110b&modify=1
When transiting through Germany with an expired visa issued by Australia, Bulgaria, Canada, Cyprus, Ireland (Rep.), Israel, Japan, New Zealand, Romania or USA, the visa must be valid when departing from the country that issued the visa.
You can also check on the IATA site https://www.iatatravelcentre.com/