The package appears to accept the global X flag, however it is not honored as dependencies are required with hardwired X flag. Reproducible: Always
Really, I think it's more that X should be called gui or something, as it just controls XDG bits. I don't think the X deps on any of these things are necessarily then optional.
The X USE flag enables `xdg` in the FEATURES variable that's passed to emake. The only purpose of it is to install the icons and all of the desktop files for gui menus. However, if the 'jack' USE flag is not enabled with the `X` flag, it doesn't install any binaries referenced in those desktop files. So launching any of those programs from the desktop entry results in something like "Could not find the program 'lsp-plugins-multisampler-x24-do'", for example. It makes sense to keep the X flag, or whatever named flag that becomes, because there are a tremendous number of desktop entries that get dumped in the "Multimedia" category that some users would prefer to avoid. But including `xdg` in FEATURES should depend on both that flag and the 'jack' flag.
