Didn't watch that much of the Olympics, but heard a lot about Biles' decision both pro and con/reasoned and venomous.
All I can say is gymnastics is the cruelest sport in the world and it only gets more and more cruel as these athletes reach higher levels of competition. My daughter was in club gymnastics until she finished seventh grade. She reached Level 9 (two levels below Elite where the sifting for the Olympics begins) and placed quite well. But at Levels 8 and 9, she was practicing 25 hours a week and I was starting to observe a Svengali dynamic between her and her coach. Her coach left the gym she was at (and tried to convince my daughter's mother and me that she should follow him to his next destination). She changed gyms and really didn't like the coaching approach (and they were insisting she repeat Level 9 even though she had finished second in the state the year before), so she decided to hang it up. She grew four inches her first year out of gymnastics. She went over to the much less arduous high school gymnastics and did very well (even won the state all-around title as a junior).
I don't know why Biles went back to the Olympics in 2021. Whatever pressure she felt was unwarranted. But that doesn't mean there weren't people putting pressure on her. It's a sport that requires this odd mix of daring athleticism and total Zen. If those girls think, they inevitably mess up and when an athlete is attempting to successfully perform the types of maneuvers they are expected to perform, it does become extremely hazardous.
Like almost everything else in the culture these days, Biles' decision took on dimensions well beyond its isolated importance. To me, that's the biggest problem.