The spreadsheet app looks like a really nice boiler plate. I was surprised to learn about this amazing library digging through the docs: https://github.com/handsontable/hyperformula
Yes, Hyperformula is amazing! it's actually the primary reason TinyCld is AGPL vs MIT, doing so was totally worth it in order to be compatible with it's GPL3 license.
HyperFormula was the key to unlocking the entire spreadsheet, the technical foundation of sparse rendering and multi-user interactions were easy enough with Yjs and and a few other libs, but I was completely stuck on how to support formulas beyond simple SUM and such until I found it.