Warning: SPOILERS for Star Trek: Picard Season 2, Episode 4 - "Watcher"
In Star Trek: Picard season 2, episode 4, it's certainly confusing why Guinan (Ito Aghayere) didn't recognize Jean-Luc Picard (Patrick Stewart) but it's not a Star Trek: The Next Generation plot hole. Picard beamed to the coordinates Dr. Agnes Jurati (Alison Pill) stole from the Borg Queen (Annie Wersching) but instead of the Watcher, Jean-Luc found himself back at 10 Forward in Los Angeles. However, the Guinan Picard met in 2024 had no idea who he was, which seems to violate the events of Star Trek: The Next Generation, but is a result of Q (John de Lancie) altering the timeline in Star Trek: Picard season 2.
It was established in TNG that Guinan is Jean-Luc Picard's oldest and most trusted friend. The El-Aurian bartender actually lived on Earth for at least 130 years between the late 19th century and the early 21st century. At both of those points in time, Picard encountered Guinan. In the TNG two-parter "Time's Arrow," Captain Picard and the crew of the USS Enterprise-D time-traveled to 1893 San Francisco and met Guinan (Whoopi Goldberg). This is, chronologically, the first meeting between Guinan and Picard. Technically, in Star Trek: Picard season 2, Guinan should have remembered Picard when he arrived at the Los Angeles location of 10 Forward in 2024. Yet it was perplexing why this younger version of Guinan - the first time the El-Aurian was played as an adult by someone other than Whoopi Goldberg - had no idea who Picard was.
The reason that Guinan didn't know Jean-Luc in Star Trek: Picard season 2 is that the events of Star Trek: The Next Generation - or any of Star Trek - never happened because Q changed the timeline. Because of Q creating a time divergence in 2024, all events going forward led to the rise of the Confederation of Earth instead of the United Federation of Planets. Therefore, since TNG never happened, neither did "Time's Arrow," and Picard and the Enterprise crew never time-traveled back to 1893 San Francisco to meet Guinan, Mark Twain (Jerry Hardin), and Jack London (Michael Aron). Guinan may still have been in San Francisco in 1893 and continued on Earth to establish 10 Forward in Los Angeles by 2024, but she never met Picard in the past because Q changed the future.
The fact that Guinan is played by a different actress in Star Trek: Picard season 2, episode 4, "Watcher," naturally adds to the confusion. It's understandable if audiences assume Guinan was also somehow changed when Q altered time. After all, Whoopi Goldberg also played the young Guinan in TNG "Time's Arrow." While it may still be possible that Ito Aghayere is playing a different version of Guinan, it's more likely that the passionate El-Aurian in "Watcher" is the same character played by Goldberg, and Star Trek: Picard's producers made the decision to cast another actor as the young Guinan instead of employing digital effects to de-age Whoopi Goldberg or have a CGI version like Luke Skywalker in The Mandalorian and The Book of Boba Fett. Unfortunately, Picard never mentioned the events of "Time's Arrow" to Guinan to help clear the audience's confusion up.
Ido Aghayere cast as the younger Guinan also creates a stark contrast to the aged Jean-Luc Picard in Star Trek: Picard season 2. This is likely by design when one remembers Whoopi Goldberg's Guinan saying how she aged herself on purpose to put her human customers - and Picard - more at ease. The younger Guinan in 2024 is also remarkably frustrated with humanity and angry in ways Goldberg's Guinan never was, but Picard was able to use the future Guinan's words to touch upon 2024 Guinan's trans-temporal awareness, bridging both versions of the El-Aurian. There are obviously further implications to the timeline if none of Star Trek happened as Trekkers remember it, but isolated to Star Trek: Picard, Guinan's history with Jean-Luc is a side effect. And it stands to reason that Guinan in 2024 doesn't have memories of Star Trek's Prime timeline the way Picard and his motley crew do because Guinan hasn't lived those events yet when Jean-Luc finds her in Star Trek: Picard season 2, episode 4.
Star Trek: Picard Season 2 streams Thursdays on Paramount+.