From Wikipedia:

“Neckbeard” is a pejorative term and stereotype for an adult man or teenage boy who exhibits characteristics such as social awkwardness, underachievement, or pretentiousness.

And incels are described as:

An online community of young men who consider themselves unable to attract women sexually, typically associated with views that are hostile toward women and men who are sexually active.

Certainly not related communities but could conceivably overlap. Not surprising that a lot of Internet trolls fall into one of those categories.