My biggest issue with Will's arc reguarding his queerness is NOT that he didn't end up with Mike, but the fact that the writers centered his queer arc around Mike, used it to traumatize Will, knowing that there would be no real pay off to his suffering.
Will Byers' queer arc arguably starts in the first season, when it is revealed that he has been the target of homophobic bullying not only from his classmates, but from his own father as well.
This is never properly addressed.
In season 2 Will was supposed to be seen pining after Mike during the Snowball. This scene was not included, but I think it's reasonable to say that this is where his crush on Mike starts.
In season 3, Will declares that "he is not going to fall in love." I have always interpreted this to mean that he thinks he will never be in a true reciprocated, loving, romantic relationship. But even if the writers meant it as a "hehe he's already falling in love with mike," this internal conflict was never handled correctly. It would just be used as something to further traumatize him in the coming seasons. Ex: Van Scene
Then he gets into a fight with Mike where Mike infamously says: It's not my fault you don't like girls. No matter what you think Mike meant by those words, whether it was projection, homophobia, or just him rudely telling will that he needs to grow up, there is no question in how Will interpreted what mike said. And sadly, that idea of will just "not liking girls" is how they choose to show Will's queerness in seasons 4 & 5.
For example in season 4, one of the first things we see from Will is him shying away from a girls flirtatious advances. In season 5 the words he uses to come out are literally "I don't like girls," instead of "I like boys" or "I'm gay." Which based off of what we see on-screen, that seems to be completely true. He is always seen either pining after Mike or pulling away from a girl. For a while I could not properly articulate why I felt off about this depiction of being gay until I saw a video about a woman talking about her experience being a lesbian and she basically said "I am not a lesbian because of my dislike of boys but because of my love for women." Which made me have this realization that the writers of Stranger Things depict Will's queerness this way not because they want queer representation, but because they want straight audiences to be able to relate to him.
With that being said, why then do I have a problem with Mike being centered in Will's sexuality journey? Will's love for boys is being depicted, so what's wrong with that?
Well, that would be completely okay if the writers didn't use Will's love for mike as a way to exploit his character, traumatize him further, and use him as a tool for heterosexual couple's broken relationship.
Stranger Things has a problem with introducing heavy topics purely for shock factor. In the last season alone they showed Will being SA'd by Vecna and hundreds of pregnant women being abused and tortured, for no real reason plot wise other than to be like "THESE ARE THE BAD GUYS!" But then they are never properly addressed again or handled with the sensitivity that they deserve. In my opinion Will being gay and being in love with Mike is just another extension of that. They wanted to introduce a really complex storyline to add on to will's trauma, but they never wanted it to actually have any effect on the main straight couple of the show.
Furthermore, if Will saying "I don't like girls" in his coming outside was truly a call back to the rain fight (which would not be much of a reach because the camera literally pans over to mike looking guilty after Will says this) then the writers were taking an incredibly personal moment for Will and AGAIN making it about Mike. Not to mention that the coming out scene was caused by a vision VECNA showed Will, that we as an audience never got to watch. Why? Well, I'll give you a hint: It's not because the writers care about Queer representation.
Even Will's "happy ending" that he gets in the epilogue is still centered around mike, because mike is the one that is saying that Will is going to meet "Cute College Boy" (The actual name listed on the IMDB cast list by the way). But that whole scene is literally just Mike saying what he THINKS is going to happen. Will having an epilogue boyfriend is compleyely fine, but it's not even really "real' in-universe.
Will Byers and Stranger Things queer audiences deserved so much better.