Genderists often fall into this logical falacy.
I'll repeat and expand on my reply to another poster on a recent thread.
You are, either through ignorance or malice, combining two different things.
It is disingenuous to pretend the issue with trans people is how they dress. Where there is an issue about dress, the issue is the reason they dress this way and the access they claim because of that.
How someone chooses to dress is, as you say, no one else's business as long as it's not indecent for the context such as wearing extreme fetishwear in Tescos, or something offensive like a T shirt with a sexist or racist slogan.
Conversely, a person of one sex claiming to be the other sex, or the right to be treated as interchangeable with the opposite sex, because of how they think is unacceptable sexism regardless of how they dress.
So far, two different things, yes? People of either sex can wear whatever they want. People are not interchangeable with the opposite sex for any reason.
The place where "wear what you want" becomes more complicated is when the point of the clothes is not enjoyment of the look, feel or utility of the clothes themselves, but that they symbolise the opposite sex, either in fetishistic terms or in identity terms. It's not the clothes anymore but the cross dressing that is the attraction. Indeed, if the same clothes suddenly became entirely acceptable for ones own sex as well, the desire to wear them would go, replaced by some other symbol of the opposite sex.
It's the difference between a man buying a fabulous women's dress because there's nothing like that for men in the market today and having the dress altered to fit his male body, and a man buying a fabulous woman's dress because he thinks he is a fabulous woman, and altering or agumemting his male body to fit the dress.
So (and feel free to check my posting history) while as a Gender Critical Feminist I would welcome a future where clothes are not gendered at all, and not sex sepcific beyond what is needed to accomodate our physical differences, as a Gender Critical Feminist I also recognise that where we are today, in a culture where both genderist and sexist beliefs still exist and often overlap and reinforce each other, clothes do carry meaning beyond their look, feel and utility and it is not somehow "not GC" not to recognise this.
You asked "Is it okay for men and women to dress as femininely or masculinely as they want, or isn't it?". The simple answer is that to a GC Feminist, clothes should not be "feminine" or "masculine" in the first place.