Thanks, Stephen!
I actually had wanted to show how absolutely terrible some services are at showing photos properly. Example:
…but the article was already insanely long, so dismissed the idea.
Good that Flickr supports 6K, but I’ll add the critical note that a proper display of photography should have no resolution limitation at all. There are zero technical reasons to do so. Including something insane like a 300MP panorama. So not impressed with 6K, although relatively speaking it’s of course great. Anything helps.