First of all sex is a term that encompasses many different organisms.

There are organisms whose sex is binary, but are not sexually dimorphic. Wikipedia has an image of two pheasants (the colourful male & "plain" female) as an example of sexual dimorphism, but as we all know, not all species that reproduce sexually are sexually dimorphic (like rabbits). Dimorphism in humans are the physical differences that can be observed between men & women: women have breasts & men having beards for instance. Human children are no sexually dimorphic, this does not affect their sex, which is binary.

People sometimes use exceptions to the rule of dimorphism (men with breasts & women with facial hair) as "evidence" that sex is not binary. These people are confusing sex with dimorphism. medically transitioning does not affect a person's sex whatsoever. Ova remain ova & sperm remains sperm.

Gametes have nothing to do with dimorphism.

This binary vs. bimodal debate is totally irrelevant to the issue. Either way trans-womxyn's sex is unambiguously male, not even intersex & certainly not female.

It's just a way to undermine the differences between the sexes & distract from the fact that there are no significant differences between trans-womxyn & men, likewise no significant similarities between trans-womxyn & women & therefore no justification to distinguish between trans-womxyn & men, & no reason to group trans-womxyn with women.

In truth sex isn't the end of the story. The sex of a person determines their socialisation, which determines their behaviour. Trans-women's sex is male, which lead to them receiving male socialisation, which lead to their male behavioural patterns. For instance: men outnumber women in media, high positions & crime, just like how trans-womxyn outnumber trans-men in media, high positions & crime.

Trans people's behaviour is sex-congruent. Trans-womxyn are not only biologically the same as men, they are socially the same too. Attempts at superficial mimicry don't change that.