I just came across this project, it seems very cool!
Looking at the code base quickly, it seems that the server is written in Django but there is a special server for Yjs written in TypeScript. I don't know the motivations for choosing to have a special server in another language, but you may want to look at pycrdt, a Python library providing bindings for Yrs, the Rust port of Yjs. Pycrdt is used for real-time collaboration in JupyterLab.