Matt Schultz wrote: …All animated gifs in my huge ANIMATION ƒ in PHOTOS have been flattened to either JPEG or PNG files. A collection of more than 40 years of animated art smashed.
I have some gif animations in my files, but I'm pretty sure I don't keep any in Photos Libraries, so I can't test anything.
Have you tried to use File>Export>Export Unmodified Originals? It may be that the originals are still intact even though the version you see on the screen has changed. This is your best hope!
Do you use iCloud Photos? There's a slight chance the Original files would continue to be OK there.
Have you done computer backups? You could probably recover the files from those, but you might have to find a phone with an earlier iOS to restore them to.
If you made an iCloud backup before the update, and if it hasn't been replaced, and if you don't use iCloud Photos, then you might be able to restore that to an iPhone with an earlier iOS.
Unfortunately, if you don't keep your own backups to an external drive, then there's no place else to look. Appealing to Apple doesn't typically work-- they tend to just remind us that we were told to backup before upgrading. It's worth a shot-- since this is a whole class of files, they might--might--be willing to work with you. I'm thinking that there's nothing written down anywhere that warned us that gif animations were at risk.
Please let us know what you find!