I use arch, with keyboard layout “es”, because I’m Spanish. My keyboard doesn’t recognize the key “Insert”, unless Fn is enabled, and I don’t know why. I found its keycode in xmodmap -kpe: keycode 118 = Insert NoSymbol Insert NoSymbol Insert.
Since Fn takes the 7th place, I thought about changing it to keycode 118 = Insert NoSymbol Insert NoSymbol Insert NoSymbol Insert, but nothing changed.
It is strange since changing it to keycode 118 = slash NoSymbol Insert NoSymbol Insert, will only work when Fn is enabled as well, meaning that Fn+Insert = /.
Probably unimportant: There’s also a keycode 90 = KP_Insert KP_0 KP_Insert KP_0 KP_Insert KP_0, but I don’t know what key is. Using xev and pressing Insert with Fn enabled says it’s key 118, so it shouldn’t be an issue.
That would be the -/_ key, or the =/+ key. There’s no +/- key.
As with my response to @palordrolap, I woke up at 4am, having gone to bed at just past midnight, and had several beers after a tough shift, then assumed (obviously incorrectly) that I knew what I was talking about. Sorry for my error.