why don't you let him grow his own hair instead of cutting it? It would be way easier if he realized that boys can have long hair as well as girls, instead of carting a scarf everywhere? The scarf is just silly. Just grow his damned hair.
ds1 wore his sister's clothes until he went to school and learned to walk in barbie shoes. He breastfed his dolls and pushed his dolls to nursery in his dolly pushchair. He went to ballet classes and out-girled everyone. (He also taught himself multiplication before his third birthday, and played 'shopping' by working out change. His nursery tried to get the LEA to assess him as he was scary bright.)
He's 16 now. All masculine. And no longer insists on wearing a leotard and tights and playing with dollies (although he still loves dance and drama). At the time, all of my friends took it for granted that he would be an entirely effeminate gay man (because largely, trans hadn't been invented on the mainstream stage for children, then. These days they would have been encouraging me to get him to the doc). He's very straight. And has the girls falling all over him.
In contrast, dd2 was a very girly girl. Long blonde hair, plaits, dresses. SHe's now 14 and vehemently non-binary. She wears grey sweats, baseball caps, and has her hair shorn. She finds her female body traumatizing. The jury is out on whether the you tubers will get her and send her a free binder.
For you, I would start with letting him grow his hair, because boys can have long hair too. But I would also be gently insistent that boys can't become girls, darling. If you teach your 4 yo that it is possible for him to become a girl, then he will believe it. (and that is a lie - he can grow up to become a dysphoric man -- that may find that genital surgery or a boob job gives him some mental ease - but he can't 'become' a woman.) You need to be allowing him to learn that all of the girly things he likes are fine for boys to like too.
And later on. Much later on. If he exhibits gender dysphoria. Then you can seek the mental health treatment he might need to come to terms with it. Which might lead to irreversible surgery, etc.
AT 4? He needs to know all of the stuff he likes is fine for boys. And that he is a boy.
(all of my three have been though the 'I am the opposite sex' phase. It's an entirely age appropriate exploration of societal roles, and learning who they want to be. Boxing them in to gender roles isn't progressive. It's regressive. If he grows up into a gay man, great. If he, sadly, ends up with gender dysphoria, then he will need mental health support. It's not an easy life, and it isn't one that you should be encouraging at 4. Particularly not when taken to its extreme, he will end up on puberty blockers that haven't been tested for long term outcomes, surgery, and sterilization. It's trendy. But it isn't a route you want to lock yourself into with a child that is exploring the world.)
I would be super careful about approaching a professional at this point. No-one is allowed to speak up, so he'll be socially transitioned before you know it. I wouldn't be taking those steps at 4, because you will set him on a path to transition, whether that would have been the outcome without 'treatment' or not. He sounds like a perfectly normal little boy. You can change that by transitioning him if you want to. But it would be your choice to do so. Your role as a parent is to gently distract from make-believe, not to cement it, which will only end up in disappointment later.