Think it seemed to change in the US around 1990-ish where the clothes started getting baggier.
I was watching a porn video from 1970 several years ago (can't find it anymore) of a college-aged orgy, maybe 30-40 people, and every guy and girl wore briefs, mostly white, and many guys wore bikini style briefs.
Back then boxers were grandpa underwear because they covered everything and many kids who wore them would get teased.
When I grew up in the 00s, I was one of the few who wore briefs, at least at urban schools. In rural schools, briefs were still fairly popular. I remember in 5th, 6th grade, we'd sometimes talk about the kind of briefs that we wear hahaha. Last decade and now you see more briefs in locker rooms, and now styles seems to be getting more form-fitting again.