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PNG has been updated for the first time in 22 years — new spec supports HDR and animation
(www.tomshardware.com)
This is a most excellent place for technology news and articles.
Probably most notably the iOS photos app until like 2014.
Edit: just checked. iOS 11 in 2017 added gif support to photos
I’ll also add, safari supported animated gifs for a long time before that and you could still save them in safari like any other image. But photos would only show the first frame like you said. When 11 came out they played like normal.