Star Trek: 10 Things We Now Know About The Temporal Wars
9. Ancient Races
Though the Temporal War is primarily fought between beings that exist on the more straightforward plain of existence, the nature of the conflict brings in beings from other dimensions and times. With the Sphere Builders (more on them coming) involving themselves in affairs, what of the Ancient Races of the universes?
While many faded long before the Wars began, like the Preservers, the T'Kon Empire, and the Progenitors, the Q Continuum were active in the affairs of the Galaxy until at least 2590.
Though Kovich says in 3190 that there hadn't been dealings with the Q for 600 years, that would mean the last time they were seen was within a few years of the Battle of Procyon V. This event both exists and doesn't, as it was a possible future shown to Captain Archer by Lt. Daniels.
What happened around these years to drive the Q into hiding? Or, at the very least, have them veer away from contact with the Federation? With the apparent death of Q in Farewell (let's be linear for a moment), they may have simply lost interest in humanity. After all, Ríos did cite Picard as the Federation's chief point of contact with the Q.
Now, The Last Generation throws a slight spanner in that thought when Q introduces himself to Jack Crusher, though of course, this may be a younger version of the same deceased eternal, so who is to say that our favourite omnipotent being didn't silently observe the greatest conflict of the Milky Way Galaxy?