Genuinely don't understand why people are pretending not to understand what 'womanly' and 'manly ' mean, or why if they were given a load of personality traits to organise according to how society sees women and men they wouldn't full well know which attributes to put in which category. And yes, OP is right telling a man he was 'womanly' would be insulting, as would telling a woman she is 'manly'.
I think manly is a more common used term than womanly - as in manly men. Yes the word 'masculine' could also be used but outside of this thread I've never seen anyone pretend not to understand what 'manly' is and in the real world and general conversation I bet more people would say 'he's very manly' rather than 'he's very masculine'.
Womanly and feminine are more different than manly and masculine, I think. Whereas 'manly' is used to mean rugged, chopping wood, fixing cars etc (masculine pursuits) 'womanly' tends to be more used as a physical descriptor 'a womanly figure' - hips and boobs, very fertile looking as opposed to a 'boyish' figure.
I think the female equivalent of 'manly' is 'girly'.
And I think there's a lot to unpack in the fact that whereas manly can cover a whole range of behaviours and actions, womanly is more limited to her body - and when it comes to the descriptor of 'feminine' behaviours and actions we default to the word for a female child instead of an adult. Manly men and girly girls.
We limit a woman to a judgement on what she looks like - if she is adult enough to bear children - and infantilise her actions.
But the reason being 'manly' as a woman or 'womanly' as a man is considered bad - when to be a womanly woman and a manly man is good - is just society's need to keep everyone firmly in their little box.
Of course a woman with 'manly' attributes (such as all the literary heroines mentioned upthread) might be treated with respect for their brains - because 'manly' is better than 'womanly' so she is acting up. She is dangerous because she is transgressing boundaries but she is at least better than everyone else of her sex. Whereas a man acting 'womanly' is degrading himself by acting like the weaker, stupider sex.
It's interesting that those literary heroines are specifically unattractive - as if by transgressing the boundaries of behaviour they are made monstrous. Jo is given suitors despite being plain, Marian is definitely not. Jo was written by a woman though and Marian a man - perhaps Louisa May Alcott thought that just because a woman was plain and headstrong it did not make her unloveable, whereas Wilkie Collins could not conceive of such a notion. Marian is respected for her male attributes, but she cannot be loved or desired.
Being called 'manly' as a woman is an insult, despite manly being higher up the hierarchy, because it means things like strong and aggressive and rough and course, and we live in a society were women are primarily valued for their beauty. To call a woman 'manly' is to call her not beautiful and that diminishes her worth - hence why Walter very much enjoys Marian's company but would never consider marrying her. He wants his wife - his woman - to be pretty not clever.
To call a man 'womanly' or 'girly' is an insult because it takes him out of his place in the pecking order and degrades him to the lower category. He is now with the support humans are only good for nurturing, cooking and fucking. The important stuff that makes the world goes round is achieved by the manly men, and requires manly attributes to do it - the attributes little women are incapable of. To call a man a woman is to make him unhuman.
of course this is all very outdated and we all know on an intellectual level that it is a nonsense, that a man can be nurturing and that nurturing is important and that women can have brilliant minds or are capable of chopping down trees and that's all great too. But knowing and believing are two different animals. Some things just run too deep for facts to get in the way and the words 'manly' and 'womanly/ girly' still hold their sway with a large percentage of the population.