There were some high level monsters in the books, especially later books; but there were very few high level adventures for 3e. (Of course, there weren't many adventures at any level, but that's another thing.) And like I said, there was never a published epic level adventure, except for a single epic adventure in Dungeon, as far as I can recall.
I will say that the high level adventures we got in Dungeon during the 3e era were some of the best designed high level adventures I have seen, though. They really leaned into some important design principles for high level adventures, such as "assume that high level pcs have high level abilities".
Even so, there was, as is usually the case for dnd, a LOT more support for lower level stuff. I think almost all the high level adventures were in Dungeon (though to be fair, there was a real dearth of published adventures from WotC in 3e period).
Again, there were almost no adventures for high level characters, and what there were were... well... let's just say that 4e's adventures were largely awful. There were a few gems among the muck, but the high level adventures were not among them. I could go on at length about the delve format that all the early 4e adventures were pushed into, but let's just say that they focused on encounters to the point of overlooking pretty basic elements of the adventure as a whole. (Keep on the Shadowfell has an infamous encounter at an excavation site that is supposed to be important, but it makes no difference whatsoever to the adventure as a whole if you just skip that encounter completely, to point at one particularly egregious example off the top of my head.)
4e's epic tier rules were great; but the game never really used them to any degree. Epic destinies were an amazing innovation- but nobody did anything with them. It's a real shame, too; they added a layer to dnd that made epic level characters very important and very special in a way that no other edition has done.
I would disagree, but I agree that it is probably the edition with the least high level support.