Oh, it is a bug of the derivation, here
The ${placeholder "out"}/bin should be removed to keep the path relative, as advised here What is the recommended use of makeDesktopItem? How to setup the icon correctly? - #6 by zarel as it allows better theming, wrappers by users etc. Right now, the issue is that makeDesktopItem will create first a different derivation, as seen in your screenshot, that contains wnly the desktop file, so the placeholder will point to this nearly empty directory.
I don’t have a computer with me right now, but it can be a nice simple first pull request for you if you want to get involved in nixpkgs. If not, just create a new issue in github with the maintainers of the package (cf names at the end of the above link) and me in mention, explaining what I just explained above.
And right now, you can temporarily fix your issue by using overrideAttrs, like replace anydesk.in your configuration with something like
(anydesk.overrideAttrs (finalAttrs: previousAttrs: {
desktopItems = [
(makeDesktopItem {
name = "AnyDesk";
exec = "anydesk %u";
icon = "anydesk";
desktopName = "AnyDesk";
genericName = description;
categories = [ "Network" ];
startupNotify = false;
})
];
});
)
(I can’t test but should work)