That’s exactly what I did for my Budget project. I created an Apps Script which could pull data out of Sheets including my weekly, monthly, and daily budget as well as update that data. This was exposed via HTTP and required my Google user auth in order to access (both the script and the Sheet have to be authorized for the user). From my mobile app I could call that script’s endpoint in order to access the data and update my budget from my mobile app. It wasn’t a terrible pain getting the script working but getting it exposed correctly and accessing it from the mobile app was a pain.