In mathjax \mathscr{C} gives me the character $\mathscr{C}$ that I want. There is a UTF listing for this character. https://www.compart.com/en/unicode/U+1D49E
If I copy form this webpage and paste into a notebook, it shows up as "|01d49e". It looks correct(not pretty), but acts like two characters when trying to copy and paste. That spells trouble, since it is too easy to forget that idiosyncrasy while editing.
Is there a better way to produce a mathematical script 'C'? It is very common in mathematical literature.
FromCharacterCode[119966]
converts the Unicode code to 𝒞 on Wolfram Cloud, but it returns a two-character string on the desktop version (12.2.0 for Mac OS X x86 (64-bit) (December 12, 2020)). $\endgroup$