Most of forums are dead or much less active. RFF is really the one left where it is well balanced.
I'm not on Instagram even if some are saying my photography has to be where. But it just too primitive and crowded for me. I'm not eager for likes from unknown people.
As for photo hosting nothing comes close to Flickr, still. And I could subscribe to interesting photogs just as on Instagram, but I could see photos in normal view on large screen, not something castrated to accommodate most stupid way of viewing pictures (on tiny mobile phone screen). Yet, Flickr provides mobile phone app, which I think, was way before Instagram.
Every time I want to find how particular camera, lens renders, I could find the group for it on Flickr to see large size photos.
So, Flickr for photos on-line storage and sharing some of them here (Instagram is not allowing it on purpose to keep all gulls in single flock).
While most of my photos are not visible on Flickr until I post them on forums via supported links.
And I also use Flickr for showcase of my past time with film and on the streets.