I fell off from Friends and Frasier years before they ended, partially because I didn’t have time to watch tv at that point, but for Friends it was also because I just didn’t care anymore. Not sure whether I can really say I was representative of the Xennial demographic though. The finale of Roseanne, on the other hand, was the groaner of a punchline to the hack comedian’s joke that the final season was, so it certainly wasn’t iconic either.
That scene from Fresh Prince that you picked is a great one. I made another comment suggesting Atreyu trying to save Artax, and I suppose I should add the super dark finale of Dinosaurs. Otherwise I can’t think of much else; so many of the iconic characters I grew up watching wore out their welcomes because tv execs in the ‘90s somehow figured out how to suffocate the lightning they caught in a bottle.