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.
It’s generally not taught by default in US schools, but some schools offer it as an elective and/or as a competitive sport. Maintaining a swimming pool is an expense that many schools, especially in poorer districts, cannot afford. Outside of schools, there are sometimes community swim classes at places like the YMCA, but those require the parents to be actively involved (like with many extracurricular activities) and usually are an additional expense.
Physical education is usually a mandatory part of US schools through high school (where students graduate at around age 18), and schools often offer students a selection of sports for PE - I did fencing one year and wrestling, gymnastics, and archery other years - but swimming requires more infrastructure than a basketball court and some padded mats.
In Germany the same - but swimming classes are mandated by law from grade 3 onwards, though we started going from grade 1 back then.