Instagram is still a thing; granted it pivoted from being a dedicated photo site to a social network with videos and stuff, but still, it started off as a photo website.
Photographers were using Flickr a lot, but then Google started to randomly turn off websites and they realised they put all their eggs in one basket.
Yeah, I put Instagram in a different category from Flickr even though Instagram used to major in photos more and Flickr had more of a community aspect once upon a time.
I still have a Flickr subscription but I definitely recognize that it's a pretty small-time operation and it wouldn't be a shock if it were to go away someday. I like it but I don't depend on it.
I know Google Photos, but that's still active, and haven't failed to my knowledge