Does one need to know all popular openings if they wants to be a top-level player? Let's say there is a player who knows nothing about Sicilian Defense. If they always start the game with 1. d4 or 1. c4 as white and play the Caro-Kann as black against 1. e4, it seems to me that they can theoretically be a player at the top level without knowing anything about Sicilian. Of course, they will have a problem coaching others, but I do not see why zero knowledge of the Sicilian can prevent them from being a top-level player.

Wilhelm Steinitz: I have never in my life played the French Defence, which is the dullest of all openings.
It would be difficult.
So you go into your first top-level tournament and get Black in the first round. No problem, you'll just play your Caro-Kann. Play goes 1. e4 c6 2. c4 d5 3. cxd5 cxd5 4. exd5 Qxd5 5. d4. You've just transposed into a line of the Alapin Variation of the Sicilian.
In the second round you're White and play 1.c4. Your opponent plays 1...e5 to go into a reversed Sicilian, and suddenly you're really wishing you knew something about that opening.