I've been shown photos of other people's families I've never seen in my life, soccer games, and other random photos. On rare occasions, it is inserting stills into videos from unknown sources, possibly other's iCloud accounts. Summary: iCloud for Windows is corrupting videos recorded from an iPhone 14 pro max resulting in black videos with scan lines. ICloud for Windows Corrupting videos, downloading other people's photos!?! The hope is that other iCloud users may have similar observations – or it may be an isolated case or user error (can't be ruled out). He had already reported it to Apple via feedback, but had not received any further confirmations yet.
The first reports are already a few days old – a user complained about unusual behavior on his iCloud account on the MacRumors forum on November 17, 2022.