As with all major updates to Minecraft, the 1.19 Wild Update added a new background panorama for the main menu screen. With work from Minecraft@Home, the seed used to create this screenshot has now been found.
Minecraft@Home is a volunteer project in which participants contribute their computer's resources into research projects regarding Minecraft, and regularly attempts to find the seeds used in panoramas or paintings taken from in-game.
On the day of the update's release, the Minecraft@Home team began work on attempting to locate the world the screenshot was taken in, by taking the screenshots from the game's files and building a recreation of it.
They then used the terrain features visible in the screenshots to determine the coordinates that the screenshot must have been taken at, and to feed into a seed-cracking algorithm.
Using the assumption that the seed used was inputted manually as a text string, the numeric seed was quickly found.
The text string seed for the world was later shown to be simply "thewildupdate", a fact that the Mojang developer who took the screenshots forgot about.
The seed used is thewildupdate or its equivalent numeric seed -1696067516, and the screenshot was taken at the coordinates (3820,67,553), on Java Edition.