Hello, Back in January 2024, I filed a bug report regarding a cache being kept by the macOS Wallpaper Agent. This cache contains every image ever set as a users wallpaper, and at the time the issue was reported, it never cleared, leaving hundreds of gigabytes wasted on users disks in some cases. FB13536275 This issue was ultimately fixed in macOS 15.1 beta 6, and remained fixed for the duration of macOS 15. The fix was excellent - the cache was reduced to storing just 2-3 days worth of images. Sadly, we've discovered that this issue is back in macOS Tahoe. The cache has moved locations, and once again is not clearing. We have filed this bug again, less than a year after it was first fixed: FB20636593 We develop an app called 24 Hour Wallpaper that keeps the wallpaper in sync with the time of day. This necessitates that the app regularly changes the wallpaper, which sadly now results in an infinitely growing and useless cache of BMP files generated by the system. As we waited 10 months for this to get fixed the first time, we expect to wait at least that long to get it fixed again, and have no confidence that it will stay fixed because the last fix lasted less than a year. This leaves us in a bad position, as people can't use our app without the cache growing arbitrarily and ultimately completely filling their disk. We've already had customers call Apple to complain about this, and the good news is that the support agents understand that this is a problem with macOS, not with our app. What we've decided to do is add a feature to the app that monitors the size of this cache and periodically deletes it. We're required to get the users permission the first time to do this, but after that the permission is cached, so the app can keep the cache folder clean regardless of if macOS is doing it's job or not. We haven't seen any side effects or problems as a result of doing this. We've seen other apps like CleanMyMac do this without any problems. We're wondering if there is anything we should be aware of regarding this caches behavior before releasing this flushing feature. Thanks for your time, -josh

Dear Apple, please make sure this bug gets delivered to whoever is responsible. That's all I ask. Please don't let it sit for months unassigned. This is, by far, the worst bug I've ever found with the macOS wallpaper system. FB21532401 If you own a 13" 2020 or newer MacBook pro model, set to the default resolution, and are running macOS Tahoe, macOS will significantly degrade the quality of any image set as wallpaper. When a still image is set as the wallpaper on macOS Tahoe, on some display configurations, the systems downscales the image to an incorrect size, resulting in pixelated wallpaper. The problem is exacerbated by the fact that macOS Wallpaper Agent appears to be using a less than ideal downscaling algorithm, which results in Super Mario Bros’ type pixelation (nearest neighbor) as opposed to any other reasonable modern method (like bicubic.) The issue does not repro on macOS Sequoia. Every model MacBook we’ve tested offers some resolutions with some form of this problem, but the 13” is the only one where it is notably awful. The most evident default case of this is the 13” MacBook Pro models with a 2560x1600 physical display (for example, 2020 MacBook Pro 13” (17,1.)) These models have a physical display resolution of 2560x1600, and a default scaled resolution of 1440x900. The relationship between the physical resolution and scaled resolution is not an even ratio (1:1 or 2:1), which seems to be the common condition under which this issue occurs. Repro steps: Set the systems display resolution to the default resolution - ideally on the model described above (see details on this below) Set a high resolution image (in this example 5120x2880) as the system wallpaper using any method Results: On the model described above, Wallpaper Agent will generate and display a 1440x810 image as the wallpaper. It should be generating and displaying at a minimum of 2560x1600, or more appropriately at 2880x1800 which is the proper 2X resolution. This can be confirmed by viewing the properties of the generated images in the macOS wallpaper cache here: ~/Library/containers/com.apple.wallpaper.agent/Data/Library/Caches/com.apple.wallpaper.caches/extension-com.apple.wallpaper.extension.image On modern Apple systems, the only situation in which the wallpaper should be generated at 1X is when the physical resolution and set resolution are 1:1. In any situation where the physical resolution is larger than the set resolution, the image should be generated at 2X the set resolution. As far as we can tell, this issue impacts any format, and any resolution of image, and occurs independent of the set image resolution.