Not all TRRS A/V cables are the same. You need one with the right pinout for a Raspberry Pi.
Considering the above image, you want to use a cable where the 4th band on the jack is connected to the center pin on the RCA video jack and where the 3rd band on the jack is connected to the outer ring on the RCA video jack. (If you have a multimeter you can test the continuity to map out which band goes to which part of the jack. I did that with all my TRRS a/v cables to figure out which would work.)