I do not understand how MCU Peter Parker being trans is even a theory. A theory needs to have some evidence (circumstantial or otherwise) to hint at the idea that there is validity to that theory. It’s a theory that Loki might come back to life female as this is something from the comics and he is clearly dead.
MCU Peter being trans has…nothing. It’s just a theory that’s come out of nowhere beyond Holland doing drag on a TV show. Drag in Britain is a long tradition of performance, especially on stage but it is not really a signifyer of being transgender.
I’m not even against people headcanoning this because they just want to. I’m just baffled as to why anyone would argue or believe there is anything to this ‘theory’. Maybe MCU Spider-Man will be established as trans but there is nothing at this moment to support that idea.