Not just bones. Muscle mass and the rest doesn't just disappear. In the sport i do (rugby), it's been evaluated to be a danger to players (increased risk of injury), and i would wager most contact sports are similar.
Muscle mass does just disappear in the exact same way as it does when someone stops steroids. It’s not instantaneous which is why places require 12-24 months of constant hormones.
Also you picked the one single example where trans women have been sorta kinda banned with basically no concrete justification, caused the world to roast them publicly, and then clubs largely ignored them and came up with their own rules — like France and the US changed the requirements to time on HRT and T levels like every other sport and the UK did a height and weight limit which, while odd, is actually a lower bar than time on HRT.
Outright bans on trans women will basically never be necessary when HRT is so effective. If by some chance there is a sport where it’s not enough you can start imposing greater restrictions like requiring trans women reach a certain (low) weight to shed any pre-transition muscle.
