Follow that train of thought through to the end.
You say you have no issue with Lia Thomas now being a "she".
But that's how we've ended up with Lia Thomas competing in women's swimming events.
Because we all agreed that people like Lia are now "she", and so the next step was, "Well since she's a she, she can compete in women's sports."
The International Olympic Committee said something along the lines of, "Everybody understands that trans women are women" when defending its decision to let Laurel Hubbard compete in the women's weightlifting in Tokyo. Hubbard didn't win, but still deprived an 18 year old female athlete from a developing country of the opportunity to compete.
We are in this situation because we all (or most of us) agreed that male people could be women. And the only way out of it is to acknowledge that they are not actually women, and never can be.
If you are willing to say someone is a woman is becomes very difficult to explain why that person should not be allowed in places or sports which are for women.