If you are looking for an iOS/iPadOS app my own Kalkyl 3 includes support for shared documents with real-time collaboration.
You don’t input text (but there’s of course keyboard support), instead you input tokens so that e.g sin is one token just like the digits.
WYSIWYG editing with raised exponents, root-overbars.
Arbitrarily complex unit conversions (e.g USD/ft^2 to EUR/m^2 is a single conversion) and dimensional analysis.
The app is free, but the document features are for pay (with a free trial):
Shameless plug for my app Kalkyl which I just released 3.0 of that adds functionality like this + collaborative editing and sharing, dimensional analysis, arbitrarily complex unit conversions, and possibility to define your own functions.