Making a particular thing collaborative requires a lot of knowledge about the internals of the thing you want to make collaborative. Yjs provides ready-to-use data bindings for many editors. Creating a new data binding requires a lot of work and testing. Unfortunately, it is not that simple.
If you want to do it anyway, you should think about how you can model the libraries internal data representation as Yjs data types. Then you update the Yjs types when the spreadsheet updates. And you update the spreadsheet when the Yjs type updates. This is why I call this a data binding.