There's still a lot of arguments over what kind of musculature and what types of feathers and how sparse they might have been so that actual appearance is still open to a lot of artistic interpretation, but there's increasing evidence that many dinosaurs would have been feathered. And we have fossil evidence of this for about 50 species (I think)

And for T.Rex we know that some close relatives had feathers: https://institutions.newscientist.com/article/mg25133560-800-t-rex-with-feathers-chinas-fossils-are-rewriting-the-dinosaur-story/