Reduce large System Data file on iPhone caused by OneDrive in iCloud backup

I had a large System Data file (over 70Gb) and couldn't work out why. I tried all the tricks listed, and finally wiped the phone to download from iCloud backup; no change! Then I spotted the iCloud backup included OneDrive - over 50Gb. Removed OneDrive from the iCloud backup, deleted OneDrive app, and downloaded the OneDrive app again. Backup file down to 12Gb, and System Data file under 2Gb. Hope this helps someone with the same issue. Cheers