If you haven’t watched all of Picard, “All Good Things…” (TNG season 7 episode 25) and “Endgame” (VOY season 7 episode 25), please be advised there are major spoilers.
This may come down to a personal interpretation: did the events of “All Good Things…” ever exist? There is one reason I ask this: the false positive diagnosis of irumodic syndrome. The way I see it, the events of that episode are rendered non-existent.
Jean-Luc assumes prior to his death in season 1 of Picard that his illness was irumodic syndrome. However, it is never specified in that season that he has the illness. In season 3 Jack Crusher is diagnosed with it and assumed inherited. However by the end we learn it was a condition related to his time as Locutus of Borg.
In VOY, the future timeline with Admiral Janeway appears to be connected to the anti-timeline future from “All Good Things…”. The Admiral wearing the same uniform and badge. However the big difference is that the present day Prime Voyager is aided by future technology. We do not see the influence of Admiral Janeway get reversed, only the events of her future.
So did the events of “All Good Things…” actually occur or did the temporal incursion being fixed rendered it non-existent? After all, Q was testing Jean-Luc. Only Jean-Luc had memory of what happened. Sub-question: did Jean-Luc actually have a correctly diagnosed irumodic syndrome in the anti-timeline future?
Yes. Although it is implied that the extent of the Q testing Picard was by pushing him to cause the problem in the first place, rather than creating it themselves, so that he would realise how it could be fixed, as an example of human thinking beyond their expectations.
We see in Trek that the future is always in Flux. While he had Irumodic syndrome in that future or something like it, in the present, it wasn’t actually, but something else like it. There may be a thousand things that could have caused it, that we’re not privy to. A space anomaly happens about once a week, and the manifestation of Irumodic syndrome itself might only have happened by chance, like the anti-time anomaly preventing the formation of life on Earth.
At the very least, in the future, there seemed to be no doubt that Picard presented with Irumodic syndrome, enough for his time-jumps to be considered just one of the symptoms.