Start digging through your Microsoft account online. I found out the hard way that if you sync any folders to OneDrive, the update can actually delete files from the cloud too, not just your local drive. @park.miles should check the OneDrive recycle bin on the web, because stuff there stays for 30 days even after it vanishes from your computer. Also look in the "Recently Deleted" album in the actual Photos website, not the app. I recovered a bunch of tax documents that way last year after a botched Windows 11 upgrade.