Most keys don't work as mouse modifiers

[KingSupernova31]

It appears that there's only a small hardcoded list of keys that can be used with yabai -m config mouse_modifier [key]. Most of these keys already have other standard functions and trying to use them with Yabai will break things. The only one that doesn't have this problem is fn, which is all the way on the left edge of the keyboard - the most inconvenient possible location for left-handed people. It would be nice if we could use any key as a modifier, or if this function were exposed programmatically to support custom signifiers.

[KingSupernova31]

There is a workaround, which is to use Karabiner-Elements to make my desired key act as though it were fn. Not a perfect solution, because now that key will also have unintended side effects, but in practice this gets me most of the way to what I want.