I'm not sure that, if they thought about it , that anyone would claim that the Equality Act "prohibits, in principle, a facility or service from being advertised as “for women” while admitting women and trans women, but excluding other men."
Of course we can superficially envisage theoretical scenarios where it may (depending on all the details) be compliant with the Equality Act to have trans-inclusive services that are represented as "for women".
All that is required (I think??) is that there are, in those scenarios, alternative provisions which ensure that no-one suffers any detriment on the grounds of being a man, a woman, a transman, or a transwoman (or on the grounds of any other PC). For example, in a sports centre that provided changing facilities there would have to be equally usable single-sex facilities in addition to the trans-inclusive facilities. And a company providing trans-inclusive "woman only" guided hiking days would likely be defended against sex discrimination cases from non-trans-identified men if they ensured that they had an adequate repertoire of alternative walks that men without a trans-identification could choose from.
But those theoretical possibilities have something of a "so what?" character.
In the case of changing facilities, and similar facilities/services where the single-sex exemption is engaged , these theoretical scenarios would entail FOUR sets of equally adequate facilities: women only, men only, women-and-transwomen, men and transmen. Not realistic, largely because of the expense, but also because (a) women might be able to bring a sex discrimination case on the grounds that, for reasons of safety, only the authentically single-sex facility was adequate for them, and therefore they just have one facility, whereas men have two. (b) the trans-inclusive facilities couldn't, in practice, have the same labels as the actually single-sex ones (it would be confusing - and potentially negligent, if it was found to have contribute to a incident of sexual assault, where a woman entered a mixed-sex environment unknowingly )
And in relation to facilities/services (such as the hiking days) where the single-sex exemptions are not engaged, isn't it already pretty uncontroversial, that trans-inclusive allegedly "women-only" options don't violate the equality act unless non-TI males suffer detriment and decide to take legal action? Certainly we see these sorts of services all the time.
But just because they don't violate the Equality Act, this doesn't mean that such services don't break any law at all. If you advertise a guided walk as "women only" when in fact some men are allowed, you are misleading consumers, and therefore breaking consumer protection law, unless your advertising makes it completely plain (not just in the small print but prominently) that it is not, in fact women-only, ie that TiMs can attend. So, to be legally compliant, it can't truly be labelled a "women-only" option at all - those words might be present as a kind of fluff and colour, but they have to be clearly contradicted.
This is all a long-winded way of saying that not every theoretically consistent extrapolation from a single law has much significance at all, outside of a speculative discussion.