There are several approaches. Some like Fischer, Kasparov, Vachier-Lagrave played a narrow repertoire they know very well and are not afraid of opponent's preparation.
Some like Carlsen play almost everything and avoid preparation.
Do professional chess players mainly stick to one type of opening and study that one very well?
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Or do they keep a broad knowledge of all openings? But when playing white do they stick to one or two openings they are most familiar with?