I'm responsible for this character being supported in Iosevka, JetBrains Mono, 3270, and Cozette, looks like. For arguments I wanted to stick to mathematical convention like f(x) without looking like a regular variable. While the lowercase 𝕩 (subject role) is more common, uppercase makes it a function and is useful in functional programming. More visibility for the character is helpful if it means wider font support, although the real sticking point has been lousy UTF-16 handling on Windows. Like most emoji, these characters need to be represented as a surrogate pair in UTF-16, and terminals in particular often don't handle it.
I wasn't familiar with BQN. Clicked through, reminded me of APL. "OH", I thought, "I see how you came up with the name." There was a (disproven) urban legend about Arthur C. Clarke's 2001, where "HAL" was secretly a reference to "IBM", where you transpose each letter by one.
H + 1 = I
A + 1 = B
L + 1 = M
Man, BQN is a clever name. Because,
A + 1 = B
P + 1 = Q
L + 1 = M...
...well crap. That theory didn't pan out at all. Needlessly disappointed myself upon hearing that it's short for "Big Questions Notation".
Misremembered about Iosevka: I requested support for a few other BQN characters after noticing it already had the double-struck ones (https://github.com/be5invis/Iosevka/issues/870). The other three were requests or contributions (drew 3270's 𝕏 myself!) explicitly in connection with BQN.
LOL, was literally going to try entering it on the new MS terminal, and realizing I don't have a windows system readily available to use. Why don't other OSes support ALT+(numpadcode) input for special characters? No idea how to do this on mac or linux.
Anyone else want to try to copy/paste into the new Windows Terminal? It does appear to work fine on MacOS under Tabby (terminal).
https://mlochbaum.github.io/BQN/fonts.html
https://mlochbaum.github.io/BQN/help/rightargument.html