I have 3 questions which I have numbered for convenience:
1) Where does LR store the images which I import? Does it move them or leave them in place? (In Lightroom Classic for desktop you get a choice to move or simply add in situ. I don't see anything like this on mobile).
2) Does it use a) a catalogue or b) XMP files? I can't see either. (Again in Lightroom for desktop you can choose to use XMP sidecar files and then see these next to your images).
3) Related to 2) - where does it store the edits? Maybe not on the phone at all? Can I see them in the Cloud storage? Or only if I sync them to Lightroom Classic desktop?
1) It imports them into the app and syncs to the cloud. So there will be one copy in the device's photos and one in Lightroom Mobile.
2) It uses a Mobile Caralog, but you aren't mean to access it for use. Although you may be able to in Android's file system (I am an iOS user). Again it doesn't work like Classic. Management is meant to happen in-app.