Onyx does not recognize volume names with characters outside an outdated and proprietary European character set.
I habitually use Chinese names for hard drives, like 漂亮.
As Onyx is just a wrapper for diskutil, it seems to filter whatever input it gets from it, rendering 漂亮 as ?? (two question marks). As a conseqeunce, all paths are invalid, as there is no drive named ??.
As another consequence, all the information Onyx gathers is wrong, and you can’t really do anything useful with it.