I would have looked there too if I didn’t already know the answer, and it might be convenient to have the additional option to do it there sometime in the future … but what you want is in the mixer:
The advantage to having it in the mixer is you can keep the mixer window open even while in write mode, so you don’t have to go back and forth to play mode if this is the only thing you’re needing. The disadvantage, at least on Mac, is that weirdness in the QT framework sometimes makes the mixer window seemingly disappear; sometimes showing all app windows will locate it, but sometimes I’ve had to just hit the mixer button twice to re-invoke it.
Also, you are aware that you can solo a stave … or even a non-contiguous on-the-fly group of instruments, just by selecting them in write mode? There’s occasionally a bit of an art to it, but in most cases (with a few exceptions detailed in recent threads), if you select an entire measure for each instrument you want to hear, only those instruments will play back. Personally I find this a lot more useful than the mixer; in the mixer I only use those buttons when I want a semi-permanent change to go into effect.