How to stop a specific app from updating / accessing internet? How can I back it up?

I have an jailbroken iPad running iPad OS 17, that has an app that I'm afraid the makers of the app would make it into a subscription basis. The app itself is about ~300 GB (most of it app data) that I: * Don't ever want it to access the internet * Don't want it ever to update (via the App Store or by itself) * Want to back it up in my NAS in the event it accidentally does so I can restore the App and ALL the associated downloaded app data to it's current state in this iPad or another iPad How would one go about doing this? Thanks in advance