I think it's important to understand that for the entire run of the show, Nancy choosing Jonathan has been Nancy choosing herself. That's how her arc was set up. Steve could never see who Nancy was but Jonathan saw it right off the bat and he loved it. In S1, they help each other investigate the Demogorgon and Jonathan never flinches from Nancy's suggestions. Joyce gets mad at him because "Nancy could have gotten hurt". But Jonathan never considered that a reason to try and prevent Nancy from doing what she needed to do because he sees Nancy as a fully competent and equal partner, not a damsel he has to protect in any patriarchal sense. Notably, he doesn't punch Steve for Nancy because Nancy doesn't need him to; he punches Steve for Will, who does need his protection at the time. In s2, Nancy takes the lead in getting justice for Barb and Jonathan is happy to follow her. In s3, yes, Jonathan is distracted by his own economic problems. But once he realizes how important it is for him to support Nancy against people like the reporters at the paper, he locks in. And he is incredibly ashamed of having not supported her previously. And the thing is, even when Jonathan wasn't being as supportive as he should have been in s3, he was still right by her side helping her investigate. Because deep down, Jonathan always believes in Nancy, even when, consciously, he's conflicted.
And then, in s4, Jonathan stumbles. He isn't perfect. But even when he's curling in on himself and not communicating and, frankly, not letting Nancy make a choice that she should get to make, he is still doing it because he is 100% Team Nancy. He loves her ambition and her drive, two things that most men of the time hate or ignore in a woman (s3 emphasized this). And he would rather not be with her (and numb how sad that makes him with drugs) than risk her brilliant future.
I understand being Team Solo Nancy in the context of the audience caring more about which boy Nancy chooses than the character herself. That makes sense. But I just think it's important to understand that, within the context of the show, being Team Nancy and Team Jancy is basically the same thing. That's just how the story has been set up since s1. Right or not, desiring a romantic partner is a fundamental part of every character's arc on the show. And within the context of Stranger Things, having a loving partner who supports you, sees you as a complex human being, and understands the importance of actively championing your abilities against sexist men, is not the same as participating in institutionalized patriarchal, misogynist norms. Jonathan is and always has been Nancy's no. 1 stan and supporter and i suspect he always will be, whether they're together or not.