Please turn off the Lightroom mobile app from the cellular data settings.
this doesn't make any difference, LR Mobile is still transfering data via cellular net. And I have Android not IOS. In Android I cannot complete disable/forbid cellular connection for one special app.
Here are two screenshots. In the first screenshot you can see that cloud sync ist paused because I'm not in the range of a WiFi net and the option Sync only over WiFi is turned on. In the second screenshot you see the limited options of celluar data connection for Lightroom app in Android. As you also can see there were nearly 50MB of data transfered for the four test picture I took a few minutes ago.
In my opinion there is a huge bug in the Lightroom app for Android regarding the Sync only over WiFi switch.