“there are far more than two sexes”
And what are these other sexes called? What are their identificable characteristics? How do they reproduce? What gametes do they produce if not sperm nor egg? What chromosomes determine sex beyond X and Y?
They have many names at least from a medical perspective (Ie turner's) but the umbrella and preferred term is Intersex. I can't speak for intersex people on how they feel about terms like Turner's or Kleinfelter's (examples of intersex).
Biological sex can be defined by the following:
1. Genitalia and reproductive anatomical development and presentation (ie gyectomastia, alternative uteruses like a bicornate uterus, mixed genitalia, etc)
2. Sex hormones (ie androgens and estrogens)
3. Sex chromosomes. We typically think of female as XX and make as XY but it's far more complicated. There are many different combinations from X, X0, XXY, XXX, etc. There are even XY individuals who are born what you may consider "female" anatomically due to failure of the Y chromosome/other genes to go through male fetal development. There just is not Y or YY (an X chromosome is required for life).
4. Sex can also involved sexual reproduction and fertility.
Biological sex cannot just be simply defined by XX is female and estrogen and male is XY and androgens. Sex is defined by many different aspects and is complex. Intersex is a wide spectrum falling outside of what you consider the binary. To be intersex is very common as well.
Sex is also an emerging research concept on its ability to affect disease and cancer (ie sex specific transcripts from the chromosomes, pathways influenced by sex hormones, pathways that may differ between sexes for whatever reason for unknown pathways), which again is very complex and nuanced (this is my PhD focus and I'm happy to talk about it)
So that's a short summary any other science fellow or intersex ppl and etc are free to add on. And I can provide any articles and resources youd.need anon. I'm trying to take you at face genuine value and assuming this isn't bait.