The Sissy Squat has nothing to do with effeminacy. It is short for Sisyphus, the God of huge thigh muscles.
Back in the old school, some bodybuilders noticed that doing back squats, pulls and other exercises developed amazing backs and legs, but also involved the glutes and hips (in fact, in the late 2010s women started doing squats with the deliberate aim of getting large, muscular buttocks). That's why the fitness industry tried to find something, anything to stress the muscles of the hamstrings and quadriceps without involving the hips or glutes, in order to develop a meaty Godlike thigh, and a tiny little waist and tush. The leg press, the Roman Chair squat, the sissy squat. The quadriceps extension. ANYTHING that didn't involve the King of Exercise, because God forbid you get thick and powerful, rather than muscly, but dainty.
Describing the sissy squat is pretty tricky. The gist is to do what amounts to a back bend, pushing your knees way out and leaning back, holding on to a weight for resistance, and some kind of pole for balance if you have to. image is worth a thousand words, here.
The upside is that it gives you a really great quadriceps pump, guys would walk away from it with burning thigh muscles and swear it was the best leg developer ever devised by man or God.
The downside is the insane amount of stress it puts on the tendons and ligaments of the knee. Honestly, if you hate having working knee joints and want to reduce the lifespan of one of the most important sets of joints you own, feel free to copy the move in the linked picture. The only worse thing you can do for a knee joint, apart from be the quarterback of the Washington Redskins and be really, really needed on the field even though your knee is being held together by nothing more than prayer - is to suggest to Tonya Harding that her entire life at the rink will be in vain because you're so going to smoke her white trash ass at the next Olympics.