I would argue that it was real. The brain anomaly was real, there are elements of that future that are are present in Picard, like the comm badges.Enterprise D doesn’t exist anymore - destroyed at the end of Generations. The “All Good Things” future was never real; it was Q’s fantasy adventure test for Picard.
But Picard came out of "All Good Things" making different decisions as a result of Q's test, and that changed the timeline. Voyager (and presumably other starships) experienced events that changed the timeline. So it makes sense that there is quite a bit in this 2399 that's different from the future of "All Good Things".