ok so i only think it can be the following: a b c d e f g h i j k l m n o p q r s t u v w x y z

but i unbinded G already, so it shouldnt respond to that.
i will try it anyways incase it actually works

nevermind i can change the bind in settings

what settings

I had to look through the Github lua sections to find it, and it's a bit scuffed.
You have to set gwater2_menukey to the number that corresponds to your letter, plus 10. By default, it's set to g (7th letter + 10, default value is 17)
Another example, I use "g" for stop motion helper, so I wanted to change it to L (for liquid). Therefore, the command was
] gwater2_menukey 22
L is the 12th letter, plus 10.
I don't know why it's this way, nor if there's a more straightforward method, but this worked for me.

EDIT: turns out, this doesn't persist! You may have to to put this in your garrys mod config, or do this command every time you start the game and load a map. There has to be a better way, but searching just leads here.