I'm not gonna get deep in the weeds of biology and testosterone. It's not my expertise, and it wouldn't be a productive conversation on this board. I'm also staying away from the question of "is a trans woman a woman?", because it could send the conversation off the rails.
I also acknowledge that this topic is complicated by exceptions (extraordinary athletes, below average athletes, hermaphrodites, etc). Life is complicated.
I'll stay with what I know, and I'll use the lens of competitive fairness and safety.
Prior to trans athletes being allowed to compete, it was easy to look at the record book in objectively measurable sports and compare differences. For example, times in track and field and cycling and swimming, pounds in weightlifting, hitting speed in tennis, driving distance in golf, etc. There is a vast difference in the measured performance of men v women, both in average performance and in comparison of the elites in each sport. Notably, that difference in measurable performance is universal across every sport, without exception.
Now that trans athletes are allowed to compete (allowing there are exceptions), we're seeing trans females dominating competitions in many different sports. It's happening in track and field, weightlifting, cycling, swimming, etc. Trans females are frequently winning competitions, and often shattering records along the way. That's violating the concept of competitive fairness. If it were true that blockers/drugs etc were eliminating the muscle mass/bone density biological advantages, we would not see so many dominating, record shattering performances.
As for safety, I haven't done a lot of research so only have a couple of examples; I'm sure there are more. I know about MMA fighter Fallon Fox fracturing the skull of a competitor. I've seen video of the North Carolina HS volleyball player who gave a competitor a concussion with a spike that hit her in the face. I know that there's a trend in international rugby to ban trans women from competing because there have been so many injuries, and many of the biological women are refusing to play to protect their own safety. Again, if blockers/drugs etc truly were eliminating the biological advantages, we wouldn't have examples of serious injuries and competitors being put at risk just by competing.