I was thinking about that when I was dropping my 6 year old off at some hobbies earlier - it’s pretty much expected to have learned how to ride a bicycle before starting school, and it massively expands the area you can go to by yourself. When she went to school by bicycle she can easily make a detour via a shop to spend some pocket money before coming home, while by foot that’d be rather time consuming.
Quite a lot of friends from outside of Europe either can’t ride a bicycle, or were learning it as adult after moving here, though.
edit: the high number of replies mentioning “swimming” made me realize that I had that filed as a basic skill pretty much everybody has - probably due to swimming lessons being a mandatory part of school education here.
Also american here and I learned to swim before I started preschool. But I also live in the land of 10,000 lakes so it’s basically a requirement here. So this is another one of those things that is going to depend on which state you’re in.
Oh yeah, I make no claim that any of my experiences are anywhere near universal. Basically no part of the American experience is.