Is that something in practice (and does it have a name?)? (The thought tickled my brain as QAM/PSK but for light...ish)

QAM can absolutely be used in fiber optics communication. Encoding and decoding systems are complicated (I won’t pretend to understand it), but it exists.

Example of a research paper using it: https://www.researchgate.net/publication/290224766_Investiga...

Radio is just low frequency light, so all of the same encoding methods apply as-is.