Then you have the constant issue of "women and NB only spaces" cropping up in transpaces and the likes. Me and others have criticized this at length because it is and will always be inherently transphobic to every branch of gender presentation and identity. To try and TL;DR a very complicated thing. Whatever you use to identify a woman and NB only space will always exclude a person physically or their idenity. Of course the same issues are going to be a problem for a "men's only" space. Regardless of whether it's trans or not.

Let me offer you a different perspective. Within POC spaces, there are specifically BIPOC-only spaces and those spaces largely exist because the non-BIPOC POC (eg Asians, non-Afro Latine) have problems with anti-Blackness within their communities and the anti-Blackness is pervasive enough that enough Black people feel that they need their own space separate from both non-BIPOC POCs and crackers. It doesn't mean that those POC aren't POC (although it does show proximity towards whiteness), but why should Black people put up with anti-Black bullshit from people who should know better? And as for "Black people can be Sinophobic/Indophobic too," Sinophobia and Indophobia are ultimately expressions of white supremacy and those expressions get rewarded through a white supremacist system that rewards the actor based on the actor's proximity towards whiteness. In other words, a Sinophobic Black person who does an anti-Asian hate crime isn't rewarded by crackers in the same way an anti-Black Chinese person is, so anti-Asian hate crimes and bigotry cannot be viewed in the same light as anti-Black hate crimes and bigotry.

POC spaces will inevitably "center" Black people and why shouldn't it? They, relative to other POCs, suffer more from racial oppression. That means trauma from Black people, which means there will be more discussion tailored towards the Black experience about coping with that trauma and how to navigate and survive in an anti-Black world. The POC mega in this very website is testament to this fact. Just recently, there's a discussion about how anti-Blackness bleeds into hair preference. The popular categorization of hair texture, invented by a thoroughly anti-Black cracker hair stylist of course, insidiously smuggles in anti-Blackness. Imagine that. Crackers somehow weaponized hair as yet another way to shit on Black people. And you could go on and on and on.

And with oppression comes resistance. POC spaces don't need and shouldn't be a pity party of BIPOC or every other POC being oppressed by crackers. There's plenty of room for Black triumphs, of moments in history and personal stories of racist crackers being put in their place by Black people. But those celebrations, by virtue of celebrating Black resistance against anti-Black oppression, will "center" POC spaces towards Black people as well.

To loop this back into the topic of trans people, trans space will always "center" transfems by virtue of transfems being the ones most oppressed by cisheteronormativity, which means more room in which transfems can vent, grief, console, offer advice, and be triumphant over big and small wins.