You can’t add a “Listen” button (L) to Groups or FX tracks in the Arrange window.
The option is available only for Audio and Instrument tracks, and Sampler tracks…
If you want to toggle Listen modes on Group or FX tracks, you have to do it on the MixConsole, or open the lower zone in the Arrange window.
But just a little L button on a Group track would save a step or two.
Why is this missing?