Live Photos are short movies created by iOS, that can be copied to OneDrive using the iOS app.
Currently OneDrive shows the Live Photo size in the listings, but only downloads a single frame from the Live Photo. The downloaded/transferred size is therefore smaller than the one reported by OneDrive.
More info:
https://forum.rclone.org/t/cant-mount-heic-photo-video-files-from-onedrive/25032/3
I don't think there is an easy solution/flag to do this, but you can probably use rclone check to compare OneDrive and GoogleDrive and then feed the list of identical files (--match) into rclone delete using --include-from. Please make a small test first and use --dry-run before each delete to verify correct functioning.