Trans men using female spaces

"This does create a difficulty for a person who has taken extreme steps to modify their body. It will become difficult for them to navigate sex-separated spaces. This is their dilemma. It should be explained to a person seeking to modify their body in this way that they will have to live with this practical difficulty, and that other people have rights. In most large public buildings where strangers mix, a unisex option is usually available and the practical dilemma does not arise."

This GI movement has been perfectly happy for women to have no options if they couldn't use a mixed sex space at all, or if they went to use it and found a man there who rendered the space unusable.

Third spaces will be created. Women weren't promised any kind of help on the way or a future in which they'd have their options catered for. They were just expected to go without and shut up or else. So my withers stay wholly unwrung.

I don't believe a service provider can exclude a trans identified female from female spaces unless an alternative is provided.

A service provider could also choose not to exclude trans identified females from females spaces

You might find the Sex Matters release on this helpful too:

Is the Supreme Court forcing a person who has taken extreme steps to look like a man to use the ladies’ toilets or saying that they have a right to?

The answer is no. Women who look convincingly like men and who go into the women’s toilets are likely to be just as alarming to women as actual men. They would have to explain themselves, providing personal information that they might not want to share (and that other people might not want to know).
Therefore it may not be practically possible for some trans-identifying women to use the ladies’ toilets.

The Supreme Court says that it is lawful to exclude them (at paragraph 221):
“Women living in the male gender could also be excluded [from a women’s service] under paragraph 28 without this amounting to gender reassignment discrimination. This might be considered proportionate where reasonable objection is taken to their presence, for example, because the gender reassignment process has given them a masculine appearance or attributes to which reasonable objection might be taken in the context of the women-only service being provided.”

But this does not mean they have a right to use the men’s toilets, from which they are excluded by rule. Men also have a right to privacy and dignity.
This does create a difficulty for a person who has taken extreme steps to modify their body. It will become difficult for them to navigate sex-separated spaces. This is their dilemma. It should be explained to a person seeking to modify their body in this way that they will have to live with this practical difficulty, and that other people have rights.

In most large public buildings where strangers mix, a unisex option is usually available and the practical dilemma does not arise.

https://sex-matters.org/posts/updates/the-truth-about-toilets/

That would not as a rule apply to toilets, but it could apply to rape crisis centres and domestic violence shelters.

You obviously haven't read the whole judgement or the multiple threads there have been here about it!

"Moreover, women living in the male gender could also be excluded under paragraph 28 without this amounting to gender reassignment discrimination. This might be considered proportionate where reasonable objection is taken to their presence, for example, because the gender reassignment process has given them a masculine appearance or attributes to which reasonable objection might be taken in the context of the women-only service being provided. Their exclusion would amount to unlawful gender reassignment discrimination not sex discrimination absent this exception. "

Trans men would be expected, under the ruling, to use the female toilets. Which makes sense, as they are female.

It is right. It's in the judgement.