Every time I see one of these "code together in real time" announcements I remember SubEthaEdit, which did this flawlessly 14 years ago, and released the collab part as a library that other apps can use: Coda uses (or at least used, I haven't used Coda in years) it and is/was compatible for sharing.
Oh yes, I remember we were using this among attendees at WWDC to write full notes of the talks! We didn't know each other but spread the connection parameters between neighbors.
https://subethaedit.net