Figma for example https://www.figma.com/blog/how-figmas-multiplayer-technology...

I've seen CF Durable Objects used quite a lot.

There are other emerging patterns too: https://www.instantdb.com/

Text is hard because it’s a list of characters, and when items are inserted and deleted the operations change the index of all subsequent elements.

Usually, editing a digital whiteboard is much simpler.