The drawing/canvas features in this app are built on top of TLDraw - https://www.tldraw.com/ - which is open source and well-architected for easy extension. TLDraw is showing up in a lot of wiki/notes products, another example is Logseq: https://twitter.com/pengx17/status/1552172906146398208

I think TLDraw will do for collaborative 2D editors what Prosemirror did for collaborative rich text editors.

(Disclaimer: I work at Notion)