Canada

Also why do we always hear about trans women athletes and never about trans men?

That's a matter of the psychology of right-wing hate mongers, and how easy they find it to rile people up about a non-issue.

Care to share sources for any of these claims?

I assume by "the trans athlete in swimming" you're referring to Lia Thomas. Here's an excerpt from her Wikipedia page:

In March 2022, Thomas became the first openly transgender athlete to win an NCAA Division I national championship in any sport after winning the women's 500-yard freestyle with a time of 4:33.24; Olympic silver medalist Emma Weyant was second with a time 1.75 seconds behind Thomas.

1.75 seconds is hardly "30 seconds" as you claim. Note that this is the only event she won, no one seems to care that she also placed last in the 100 freestyle event, or that even in the event that she won she was over 9 seconds slower than the women's record for 500 yard-freestyle.

As for the MMA fighter, after a quick search I'll assume you're talking about Fallon Fox? It's true she did injure one of her opponents, Tamikka Brents. I don't know much about MMA, but seeing as it's a sport where people punch and kick each other violently, I'd assume injuries happen.

Let's assume she did have an advantage as a result of going through male puberty as a teen. Where do we draw the line in regulating biological advantage in sports?

Caster Semenya, a runner who was assigned female at birth and has lived her entire life as a woman, has higher levels of testosterone than the average cis woman. Should she be banned from competing?

Michael Phelps, a cis man with many Olympic medals in swimming, has an unusually large wingspan, double-jointed ankles, and produces around half the lactic acid of an average person, all of which gives him a biological advantage. Should we rescind his medals?

Why is "unfair biological advantage" in sports only brought up in the case of trans women (or in the case of Caster Selenga, gender non-conforming women who are mistakenly assumed to be trans?)

https://www.gendergp.com/new-report-confirms-trans-athletes-do-not-have-biomedical-advantage-in-elite-sport

https://www.forbes.com/sites/lindseyedarvin/2024/04/25/transgender-athletes-could-be-at-a-physical-disadvantage-new-research-shows/

https://www.scientificamerican.com/blog/voices/stop-using-phony-science-to-justify-transphobia/