Wallpaper becomes black when swiping between applications running in full-screen

upd#2:

After spending a full day testing every possible approach, here's my findings and what actually works.

The problem

Black screen flash when exiting fullscreen apps on macOS Tahoe. Triggered by dynamic wallpapers + Reduce Motion enabled. Disabling dynamic wallpapers fixes the black screen — but then you lose the rotating wallpaper experience.

What I tried (and why it failed)

1. launchd + osascript (System Events)

Script ran, log was written, but wallpaper never changed visually.

Reason: FSFindFolder error -43 — System Events can't access GUI context from a background process.

2. cron + osascript (Finder)

Worked manually, but not on schedule.

Reason: cron on macOS Tahoe throws Could not switch to audit session: Operation not permitted — Apple blocks audit session switching for background processes.

3. launchd + osascript (Finder)

Same issue as above.

4. defaults write com.apple.desktop

Wallpaper was written to the plist correctly, but macOS Tahoe ignores com.apple.desktop — it now uses the com.apple.wallpaper store.

5. cron + Swift (NSWorkspace.setDesktopImageURL)

Worked manually, unstable on schedule — same audit session problem.

6. launchd + Swift + SessionCreate

Partially worked — sometimes SkyLight got a proper GUI session, sometimes not. Completely unpredictable.

What actually works: Hammerspoon

After all the above failed, I switched to Hammerspoon — a free, open-source macOS automation tool. It runs as a proper GUI app in the menu bar, always in the correct audit session, so it has no permission issues whatsoever.

Install:

bash

brew install --cask hammerspoon

Config (~/.hammerspoon/init.lua):

lua

local wallpaperDir = "/Users/YOUR_USERNAME/Pictures/wallpapers"

local function setRandomWallpaper()
    local files = {}
    local handle = io.popen('find "' .. wallpaperDir .. '" -maxdepth 1 -type f \\( -iname "*.jpg" -o -iname "*.jpeg" -o -iname "*.png" -o -iname "*.heic" \\)')
    for file in handle:lines() do
        table.insert(files, file)
    end
    handle:close()

    if #files == 0 then return end

    local randomFile = files[math.random(#files)]
    for _, screen in ipairs(hs.screen.allScreens()) do
        screen:desktopImageURL("file://" .. randomFile)
    end
    print("Wallpaper set: " .. randomFile)
end

-- Set wallpaper immediately on launch
setRandomWallpaper()

-- Then every 15 minutes
hs.timer.doEvery(900, setRandomWallpaper)

Replace YOUR_USERNAME with your actual username (check with whoami in Terminal).

After saving the config, click Reload Config in the Hammerspoon menu bar icon.

Add Hammerspoon to System Settings → General → Login Items so it starts automatically on boot.

The root cause of why all shell-based approaches fail is Could not switch to audit session: Operation not permitted — macOS Tahoe intentionally blocks background processes from accessing the display session. Hammerspoon bypasses this because it's a proper GUI application.

Hopefully Apple fixes the original black screen bug so none of this is necessary 🙃