The sandbox we ship for macOS is broken for a while now (see #22000 (moved)) we should not ship it anymore until we fix it as this is confusing to users and gives a broken experience.
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If I see that right we never made a distinction between the background.png and .DS_Store files we ship on master and on maint- branches when switching to tor-browser-build which means we always shipped the ones for the sandbox.
The reason why this in the end did not matter was that we (or at least I) used the non-sandboxed ones on my build box when recreating the .dmg files after signing.