Despite the odd clickbait way this has been phrased by the Indy, Starmer has actually just committed to supporting the existing (still vaguely defined, but recently clarified) EA2010 provisions while also supporting Labour's ongoing resolution to reform the awkwardly hacked-together GRA to allow self-ID.
So really, what he's actually said is: business as usual.
As one of those evil devious trans women mentioned above, who has very much benefited from the GRA and happily invisibly passed through single-sex spaces for the last twenty years and harmed precisely nobody, I'm breathing a sigh of relief that Labour isn't detonating existing protections just yet.
There aren't many of us - nowhere near enough to have an appreciable statistical impact worth catering to, politically, in comparison with much larger forces present - but we do exist, and we're perpetually cowering in terror and bracing ourselves for the caustic fallout whenever there are rumblings about GRA reform and EA clarifications, as we're both the awkward speedbump that stands in the way of the formation of the unisex gender utopia and the secret enemy within, invading the sisterhood.
'GRA reform' is one of the more frightening things to read rumbles of in the news, as that's a door that can swing multiple ways, and our voices are always lost in the shouting. Whichever way things swing, it's hard to see change as an inherent positive. Which is an uncomfortably centre-right place to find yourself standing in a polarised world where the right very clearly isn't the one that has even a shred of regard for your safety.
I'd support the provision of self-ID on principle simply because the GRA was always an incomplete hackjob that happened to be quite useful within the paradigm of the time, but I'm not sure how to square the circle and make everyone happy, and I'm not convinced there's a way to avoid the 'Brexit effect' of crystallised reactionary stances and catastrophising hyperbole from both sides overwhelming any attempts to seriously conduct a discussion about consequences.
GRA reform, right now under a Conservative government that is demonstrably hostile to the notion of reform, looks an awful lot like a great way to make things appreciably worse for everyone.
I'm not sure it actually looks much better under Starmer Labour, either.
It clearly needs to happen, but the Appeal to Consequences seems overwhelmingly strong, here.