https://github.com/zenkalia/T-keyboard/blob/bleeding_edge/ex...
except it would add a ~ rather than trigger an arrow key. I'd likely put it on sym+q so that it is in a similar space to a real keyboard.
I was discussing special characters with someone on github. If the character isn't in the font you'll have to do some extra work that I summarized in this comment: https://github.com/Xinyuan-LilyGO/T-keyboard/issues/10#issue...
In the comment above it the mapping table that I'm talking about is this one: https://github.com/zenkalia/T-keyboard/blob/bleeding_edge/ex... .