It would be most straightforward to let them sync and then delete them. However, if you did any work on these photos in Lightroom mobile, then it will be the copies that are syncing that you'll want to keep, not the ones from your One Drive. If you want to stop them from syncing, however, then delete them from Lightroom Photos on your mobile device. Photos that have already uploaded to the cloud, however, will still sync. The only way to delete these before they arrive on your computer is to go, in Lightroom desktop, into Preferences, and on the Lightroom mobile tab, Delete All Data. This will delete all that is in the cloud - the photos you're referring to, but also all that you have synced from Lightroom desktop to your mobile device. (They will be resynced, however.) In the future, either don't import the images into Lightroom mobile, or don't import copies from your One Drive into Lightroom desktop. One of the strengths of Lightroom mobile is that all that is imported into it will automatically arrive in Lightroom desktop.
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