i sympathize with your concerns wholeheartedly - though i'm a woman, i can't directly relate, but a lot of my life has been spent coming to terms with the fact that i'm not attractive. so some of what you've said here is relatable, not all.
i would advise to stay away from the incel terminology though, inceldom is very toxic and will only worsen your mental state.
i do have a few things i would like to say, though.
first, it's a hard pill to swallow, but its true: people care about physical appearance. i don't want to sit here and lecture you on how personality and hobbies can make you a better, more attractive person, because what everyone needs, first and foremost, are the looks to get their foot in the door like you said. i wish this wasn't the case. for as long as i remember i've wished that everyone was a grey blob and we formed connections based on personalities instead of looks. but that's just not how things are. for me, i've started hyperfocusing on improving my looks: going to the gym, eating right, doing my hair, makeup, washing my face, moisturizing, perfume, clothes. for men, i don't know how that would look, but if it is a real concern for you, there are ways to improve; know you're not entirely powerless. thinking that it's all hopeless is the key for falling further into despair.
however, there are some things you've gotten wrong. as some other commenters said, there are ugly people in relationships everywhere. who are they in relationships with? other ugly people. it's about understanding that you're not exempt from this phenomenon; who are the types of women you are after? and yes, i am aware many unattractive women overinflate their looks and reject men who are on the same physical attraction level as them, but reality is often different from what some patterns might suggest. all it takes is one.
and lastly, i'd like to say that not all women desire the "tall, masculine, well endowed" man. as a woman i genuinely couldn't care less if a man is tall (i'd totally be with someone 5'0), masculine, or is well endowed, lol. for me, it's more about face and personality. he could have a micropenis and i wouldn't care, genuinely! while it's hard to understand when you've been faced with such rejection and observed how vain people can be, there are people that truly, truly do not subscribe to that type of thinking. incel ideology tends to over generalize. society sucks, i agree with you there, but generalizations and saying "this is how everyone is, no exceptions" really only makes a person feel more hopeless. i know this forum is full of hopelessness but sometimes things are just plain... wrong. this is one of those times.
i'm not gonna tell you what to do. i'm telling you my opinion, and thats just it: an opinion. i know things can be tough for men, trust me. constantly thinking this way, though, is very painful, and i tell you that from personal experience. i hope that whatever decisions you make for yourself, you can one day feel better about yourself and find your place.