I think it's important that we define what an incel is first and foremost, because the word has lost a lot of its meaning over the past decade.

Incel is short for 'involuntary celibate', or somebody who hasn't had sexual relations not out of a voluntary vow of abstinence, but rather because mental and/or physical factors have made them into an undesirable partner and have left them feeling shunned by society. This could be things like autism, personality disorders, physical disfigurement or major injury as examples.

Many people in that situation refuse to identify as an incel, because the incel community which several mass shooters like Elliot Rodger came from is deeply misogynistic and talks about women as if they're subhuman. They also idolize mass shooters as heroes. So maybe incel refers to that deeply misogynistic sect of the manosphere.

But more recently, incel has become something of a catch-all insult towards low value misogynistic men. Andrew Tate for example has been branded the 'Incel King' for the views that he preaches, even though 1. unlike an actual incel this guy fucks, and 2. a real incel wouldn't have the charisma to run a MLM scheme, cam girl business and an alleged sex trafficking operation.