Biology isn’t even relevant here, we’ve surpassed evolution, there is absolutely no reason why someone shouldn’t change their gender if they want to. Apart from that, I find it hilarious how confident conservatives are about this, the situation isn’t that simple, there is a number of naturally present aneuploidies including the sex chromosomes. Even in the usual XX and XY variants, parts of the Y chromosome are homologous to X and the expression of sex-specific genes is modulated by epigenetic factors. In practice the concentrations of the sex chromosomes are not on/off and can vary fluidly. With these simplifications, you are just displaying your ignorance of biology.