Mike is a trans girl theory
Unlike Lucas and Dustin in S1, Mike immediately warms up to a girl who looks like a boy and is clearly different so he can relate to her. He showed her his house happily before he even knew she knew about Will. El's arc in S1 is very much trans coded and in many ways i believe it's analogy for Mike being trans. Mike gives a girl who looks like a boy his clothes,hides her in his closet and then his mom tells him he doesn't have to hide anything from her. Mike knows how to do make up and has sisters clothes in his basement. He gives Pink dress to El and does her make up, projecting what he wishes to be. This is even more obvious when Mike in blue clothes stands behind El in pink dress in the mirror who is experiencing girlhood for the first time. If a girl is experiencing girlhood for the first time,why putting boy behind her? Unless he's experiencing it as well and wishes to look like her. Compare this to him being rude towards Max and immediately disliking her when he meets her. Max who has a beautiful long hair and has all the boys going crazy for her and he wishes he could be her. Meanwhile Max's main song in S4 is running up that hill which is about woman and a man swapping places, queer people for years have been saying this song is trans coded. They knew what they were doing while picking that song
Mike is looking for dart in the gym and finds Max and says to her : "This is the boys room."
Mike: " So it means you should go home"
Why even speciffically saying she should go home cause it's the "boys room"? What does this have to do with him mentioning her gender now and getting so defensive.
Demogorgon looks like a vagina,the gate looks like vagina and El going through it looks like birth. Mindflayer in S3 as well looks like vagina and in S5 as well. I doubt that monsters look like female genitalia cause of the creator being gay and scared of it. Makes more sense it's trans girl experiencing gender dysphoria and we see her POV through supernatural. Even Vecna doesn't have penis and is connected to the vines like black widow.
And Mike goes to girls toilet at rinkomania looking for El and the girls tell him to get out while they're wearing pink,white and Blue(colors of trans Flag)
S3 focused heavily on gender roles like Nancy's journalist plot, Joyce does it with Hopper as well and Max&El talk about boys being terrible while they're experiencing girlhood. Mike who goes through internalized transphobia and is trying this whole season being this masculine straight dude says "women act on emotions and not logic". Meanwhile Mike says "screw logic" to Dustin in S1. Mike then get's attacked for being too emotional instead of using logic while discussing about El's powers.
S4 again shows how important hair is,they focus on Hopper being shaved while El get's buzzcut again. Meanwhile in S4 Mike has long hair,but at the beginning of S5 the party says they have to blend in and Mike is back to wearing clothes his mother buys (which looks like his dads clothes) and has short hair
Max says Holly is her brother Mike and Holly has tons of parallels with her brother. We see Holly enjoying herself in Creel house, experiencing girlhood,trying on dresses and the first dress we see in the closet is a pink dress that had the same shade as the dress El wore in S1. Why was that so important to show? Her doing this by herself and song about being alone is playing. Almost like that's what little Mike was doing while his family was away,trying on his old sisters clothes and having fun. That's why we see a scene of Mike in S1 getting scared when Karen comes and has to hide his symbol of femininity (El) in the closet. Cause Mike would try on his sisters clothes and immediately had to hide when his mother arrives. Meanwhile while El is alone in the house, wearing Mike's clothes,she goes to Nancy's room and wanting girlhood she was never allowed to experience. She represents Mike in that moment, even if their reasons for not having girlhood are different.
Since we're talking about Pink,this color is so important in the show, especially Pink/blue combination. Nancy in S1 wears light pastel colors, especially Pink and has a light pink room that screams girlhood. Meanwhile Mike's room is blue and dark, almost feels suffocating just like the masculinity that is forced on him,Mike even says "dad you're choking me" while Ted is putting a tie on him. Nancy again wears light pink colors in S5 and Jonathan somehow has to mention he threw her pink sweater cause it was Pink. Why? It was so out of Jonathans character, but i think this was a hint for Will being disappointed that Mike is trans. Vickie is dressed in pink uniform and Robin plays for her "pretty in pink" ,lyrics goes "she loves to be one of the girls"
Mr Whatsit in Stranger things is a man while in Wrinkle of time is a woman and Mike speciffically mentions that(Mike always at the scene of the crime)
In The first shadow Henry looks like he's trying on mothers dress. A vision also appears to him and mindflayer is a woman disguised as Patty who's ripping of her hair. Cast members call mindflayer "Mindy" which is similar to Mike and mindflayer is called Mindy on WSQK as well . Patty also often get's compared to Mike and is meant to be his parallel. Just like Nikki in Tales of 85.
I think femininity is even bigger part of Stranger things than homosexuality,but we confuse those things cause of the AIDS metaphors and Will being bullied for being gay. But even bigger part we see in the show is girlhood,huge focus on Nancy losing her virginity and losing her best friend,El herself experiencing girlhood and being friends with Max. Chrissy who was a first victim and had ED directly parallels Mike,they both have abusive mothers(that's a whole other theory i have,Karen is way worse than people think)and eating disorders. So much food mentions around Mike and him being called a twig cause he's a trans girl struggling with her body. Women in general had bigger roles in the show, the only male role that was big every season is Hopper who's definition of toxic masculinity.
Femininity was always bigger part of the show than homosexuality, whether it's text wise or subtext wise in supernatural form.That's why Mike being trans makes more sense.