True femcels are quite bizarre. I've never encountered one. It's some combination of obesity, poor social skills, or being postmenopausal. This doesn't happen too much. Autism is rare in females and even some amount of overweight/obese women have sexual abundance. Men are thirsty AF for sex.
What is more common among females is involuntary solitude, a phrase coined by Chateau Heartiste when his blog was active. The insol female is a female who can get laid but cannot secure a commitment from a man. She has at least adequate social skills and she's usually around average looking. She looks very normal in everyday life. You wouldn't recognize an insol female when walking outdoors on an urban walking path, in a mall, in a grocery store. An incel male stands out more in public when an incel male goes into public. They are socially awkward and can be weird looking too with things like neckbeards.
The insol female is often in her 30s/40s, childless, and never married. She is typically found living in a big city with friends who are mainly married or in multi-year LTRs. She's often on the swipe apps for long periods of time, often deleting/re-starting swipe apps/dating website profiles for 5+ years at a time. She has a lot of "one date, no sex, no second date" type interactions, some one night stands, and some situationships. Committed relationships are rare for her. The insol female can find sex when she's horniest with not a lot of effort.