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.
https://mlochbaum.github.io/BQN/fonts.html
https://mlochbaum.github.io/BQN/help/rightargument.html