Apple today released the fifth beta of macOS Sequoia to developers for testing purposes, and some Mac users noticed a new forest-themed "Sequoia Sunrise" wallpaper appearing after installing the update.
The wallpaper has not been officially released, and it is not a selectable option from the Wallpapers interface in the Settings app. Instead, it is tucked away in the system files, as noted by Mr. Macintosh.
Mr. Macintosh has the wallpaper available to download on his website, but it can also be found in macOS Sequoia beta 5 in the /System/Library/Desktop Pictures/.wallpapers folder if you want access to it early. The file is hidden, so Shift + Command + Period has to be used to display hidden files. There is a dynamic .mov version with subtle movements as well, but there is no Dark Mode version.
After you pull the image from the system folder or download it, you can right click and choose Set Desktop Picture to use it as your wallpaper.
That the wallpaper has been showing up for some users suggests that it is going to be added in full in a later beta. Right now, users who do see it after installing the latest macOS Sequoia update cannot select it and it is displayed with an "unknown" label. Not all users are seeing the wallpaper after installing the macOS Sequoia update.
