Microsoft had a blog post somewhere talking about how they're using desktop rendering code via wasm and canvas to get to parity.

Don't know how complete that effort is though. Haven't checked myself.

Google has switched in 2020 (if i am not mistaken to canvas), but I am not saying this would be the solution to everything, It is just another option one could do. I do not know if someone noticed this, but that is part of the reason you could not just open google docs on mobile. Because I would suspected that it would been too much effort for them back than. In anyway Tasfer tried as best as possible to do that on mobile too.