As mentioned in this thread. There was one release of the Eleven Rack editor and then it appeared to be abandoned, no updates. That release was officially supported on
- Mac OS X 10.8-10.8.5 and 10.9-10.9.1 (OS 10.7.5 and earlier are not compatible)
- Windows 7 SP1 and Windows 8/8.1 (64-bit only)
Now that Avid sloppy marketing in places also says things like "Mac OS X 10.8 and later" means nothing in terms of official/ongoing support.
There are no specific tricks for installing the Editor on OS X/macOS that I'm aware of. The GUI does not redraw properly on Big Sur, and maybe that may well have started happening before. Been lots of painful changes to macOS graphics and security areas in the years since the Editor was released.
And as mentioned above, this is a complex product, it incorporated iLok runtime and other components, presumably to get parts of the plugin/old built-in Eleven Editor UI up and running. It was nice for them to try at the time but it was more overcomplicated poorly supported bloatware from Avid. You really don't need it at all to use the Eleven Rack, and if you think you do, then the Eleven Rack is not for you. May I recommend the Fractal amp sim products with their fantastic Edit programs and good ongoing support.
"You"?? Avid will typically not comment on any product plans beyond publishing official end of sale/life dates (Avid pro control surface folks on DUC are a slight exception there, and great to see). I don't think they ever listed the Eleven Rack editor as a product there. Curious, but I can't check now because that web page is down... But again the Editor has been effectively been abandonware for years, for a hardware product that is no longer sold, from a team of developers and folks who were largely pushed out the door at Avid... so I would not waste my time. The Eleven Rack is a great old product, use if however you can and be prepared eventually for it to stop being usable as an interface when drivers are no longer supported (but big thanks to Avid for bumping driver support).