Need suggestion to handle processing complexity too hard in AppSheet

[Mahesh]

I am building a meal planning app that will would let me build my grocery shopping list.
My rough plan for the app is like this

1. Enter meal plan via AppSheet table
2. Invoke some back end processing logic which will create the “explosion” to give me the grocery requirements.
3. This will somehow be input as AppSheet table.
4. Use AppSheet to present the grocery shopping list

Right off the bat, I know #2 processing has complexity that would either hard to solve with AppSheet or will need extremely kludgy AppSheet workarounds.
So instead I was thinking I would develop some backend server side logic (node.js, python, etc) and let the AppSheet app to call.

But I do not know where to start.

Looking for ideas, what technology to use on the backend, that can read and process data in Google sheet. where would I host this logic and how would I invoke it from AppSheet, etc

Thanks!