This is actually a very narrow and simple term. A nonconformist arises in a social group when he is alone against everyone. When there are two nonconformists, they turn into conformists.
A "real" nonconformist will be one who seeks to swim against the tide and in any form refuses behavior (thoughts, ideas, etc.) and is conscious or unconscious. Still, I consider it wrong to single out the genuine ones among them, because the very idea of absolute protest and its "realness" will contradict and protest against itself, which leads to a logical error.
But if we take it as a starting point point to the very unmotivated desire of the individual to resist society (in simple language - to do the opposite), then it would be more correct to call such a person a negativist, but this is already a psychiatric term.
I think there are no 100% nonconformists. There are situations when you have to adjust to society or social group. But nevertheless, a real nonconformist is a person who is ready to defend his point of view under the onslaught of the crowd, even when it is very difficult. Nonconformists have their own belief system.