We switched servers a few weeks ago, and we didn't realized the FS9 downloads were missing but, of course, since almost nobody uses FS9 anymore, it took a while for somebody to notice so we could restore the downloads.
So now, at least I can assure you the Standalone Addon Manager for FS9 works and download the files correctly.
About *working* on Windows 11, that's a whole entirely different problem, which we can't offer you any support with. I know they work on Windows 10, but we don't have anybody testing on Windows 11, and nobody will work at a fix, even in case it would be discovered there's no chance to make it work.