Army of the Dead had a big Snyder Cut Easter egg in one scene, but it turns out it was way more of a joke than we realized. Early promotional images for Snyder's new zombie flick revealed the team breaking into the vault, and on the side of the vault door you could clearly see a set of film canisters with a label identifying them as Zack Snyder's director's cut of Justice League, but there was more ironic context to the scene when it finally arrived on Netflix.
Army of the Dead originally went into production in the summer of 2019, months before Snyder says he ever thought the release of the Snyder Cut was even a possibility. As a result, the movie had reached this mythic status, so the idea of making it locked away in a vault in Vegas is a pretty funny meta-joke. The canister props were also shared to social media by Snyder when he declared that the Snyder Cut was totally real and existed, giving even more meaning to the props when they were glimpsed in the film's promotion.
However, once the movie arrived, it turned out the scene from all the promo images and trailers was from a fake imagined version of the heist. Not only were multiple people there who were never even in the vault, from Damon (the guy who bailed before the mission even started) to Chambers (who was already dead by the time they got to the vault) or Peters (who was always on the roof working on the helicopter). Additionally, when the team opened the real vault, there was nothing visible other than the pile of cash, meaning the Snyder Cut was only a figment of the imagination of the heist crew.
There's certainly a bit of humor in the fact that, in the movie, Snyder presents the Snyder Cut as something that's out of reach and only in the imagination of the main cast, but the fact that Snyder posted the props to social media and many people took it as tangible "proof" of the Snyder Cut's existence makes it even more humorous. Snyder never actually claimed that's what the image was, he merely posted the image and said "is it real? Does it exist? Of course it does," which was a factual statement, and one that didn't even need visual proof as many other people from production were making the claim, and Justice League's production timeline itself indicated there was enough work done on that version of the movie.
Regardless, the Snyder Cut reels were already one of the funnier interesting Easter eggs in the movie, and it's only funnier knowing the full context, especially considering the Snyder Cut ended up being released before Army of the Dead even came out. Snyder himself may say he thought it was a dream at the time, but it just shows how quickly some things can change.