There are philosophical discussions to be had about the different ways of knowing oneself, whether the answers must be stable, whether we need to feel certainty, and what there even is to be known.
What doesn't work for me is when someone (who is almost never trans) wants to make this argument specifically to undercut trans people. Transphobes make this move all the time. They take an overall philosophical unknown and use it specifically to infantilize and undermine trans people, saying trans people aren't qualified to assert whether they're a man or woman. If the self-styled philosopher were to turn the same degree of radical skepticism toward themselves, they would have to disavow everything they feel or do, too. Yet they are only focused on trans people's self-knowledge. Hmm.
I hear them say — citing the idea that no one ever really knows themselves — that no one should be allowed to transition to another sex/gender, but I don't hear them say that no one should be allowed to marry, have kids, buy a house, choose a career, etc. which are also large decisions, the happy outcomes of which depend on self-knowledge. And allegedly they believe everyone lacks that self-knowledge, right? Or do only trans people lack it?
Blake Smith in Tablet was saying we're not very good at labeling ourselves, so, instead, we should label each other, which means to him — more specifically — that he should label trans people's genders. But he probably labels himself a gay man, right? Or have I got it wrong — does he want someone else to decide whether he's gay or straight or bi?
He published an essay in Unherd last year about sexual desire: about how, even though we don't always know exactly what we want or why we want it, nevertheless we do want it. He wrote about how he doesn't like being repeatedly interrogated Are you sure you want this? (even in the name of consent). Something that could be "as simple as saying 'yes'" becomes unattractively complicated and detached when you have "to start itemising what it is you actually want," he wrote. He feels that way about his own sexuality, yet he thinks that everyone should interrogate trans people's identities. Why can't he just accept a trans person's self-assessment that they're a man, woman, or something else entirely? Why does the trans person have to itemize the components of their being for everyone else upon demand, in complicated, repetitive ways, when they're not even in an intimate encounter in which the discussion could be of mutual benefit, but they are, say, waiting for the bus? Smith said he wouldn't have let a particular person of ambiguously gendered appearance sit with him in the high school cafeteria, and he said he wants to more explicitly call out people's gender differences so he can avoid the "cringe-inducing" genders. This is not a serious philosophical inquiry into self-knowledge, nor would I care to engage directly with a writer who would publish things like that.