What trains would that be? Street cars and busses are the only ones I can think of that don't have first class. Everything from the S-Bahn and "up" has a first class car or section.
That heavily depends on your local Verkehrsverbund, many Verkehrsverbünde do not have any first class in S, RB or RE.
In berlin neither the Sbahn nor the Ubahn has first class. The express trains (RE7, RB14, FEX) to the airport don't either as far as I remember and I don't see one when I check[0]. Similar for many other cities I believe, so I'd wager most travelers the 9e ticket is covering will be on vehicles that don't have first class anyway.