The important sign is the one on the door that says 'Women'.
Presumably the women's toilet is provided in order to be complaint with building regs, etc. Whatever the reason, the point is that it has been designated for women, and that, as the SC clarified, means biological women only.
This sign undermines the spirit of the main sign.
Nobody other than biological women has the right to use that space.
There is nothing wrong with the people who are entitled to use the space to assert that fact, firmly but politely.
For instance, as a gender-non-conforming woman, I've been 'harassed' by women saying 'Excuse me, this is the ladies!'
I felt they were doing the right thing by challenging somebody who at first glance looked like they shouldn't be there.
A pleasant reply 'It's OK, I'm in the right place!' was enough to get that second look that immediately reassured them that I am a woman - it only takes a proper look and a few seconds to recognise all the features that make a woman recognisable regardless of her personal aesthetic.
This is an established practice - anyone who at first glance looks like they are in the wrong toilet has been challenged, and it's been OK. It was understood that it was to protect the privacy, dignity and respect of the people who were entitled to use the space.
It's only because of this recent fad of men insisting on using the women's toilet that it has become problematic.