For clarity, why is it rubbish??
As others have said already, there is no law in the UK that stops anyone from using any toilets they want. That's just societal convention. There are laws, however, that govern everyone's behaviour in toilets (and everywhere else) - trans or cis, male, female or non-binary.
I feel like I'm going round in circles here, I addressed a lot of this in my post earlier in the thread. I'm aware that it's a lot to take in, especially if you're unfamiliar with the subject, so I'm not blaming anyone, but anyone who's genuinely interested might want to go and read it again (and other posts, I'm not claiming mine is the only good post!)
Secondly, currently to get a Gender Recognition Certificate you don't need to have had surgery or take hormones anyway - so that's not going to change!
JK Rowling is an intelligent woman - these things she's writing are not mistakes, she's deliberately lying. Or if she thinks she's telling the truth, maybe she should actually do some research and fact checking first, rather than just believing what others have told her.
There's a long thread here about many of the problems with JK Rowling's piece - this breaks it down very nicely:
https://threadreaderapp.com/thread/1270787941275762689.html. Unlike JK Rowling's piece, it's also backed up with plenty of statistics and other evidence.