The “western” is both aesthetic and thematic, a collection of tropes and conventions and ways of thinking about things. Yellowstone is aesthetically a western but thematically it’s more a mafia or prestige-TV-antihero program with some western elements. Mandalorian is thematically a western and also shares a lot of aesthetic similarities, despite being ostensibly sci-fi. In fact, science fiction is where a lot of “western” elements thrive - Avatar, Aliens, Firefly, Rebel Moon, etc. Gene Roddenberry pitched Star Trek as, “Wagon Train to the stars.”
This is all a gross oversimplification, of course. The fact is that aspects of the “western” archetype finds their way into a huge range of American pop culture, even when they aren’t the dominant element. Of the themes in Magic Kingdom, it’s probably the most profoundly culturally significant, the one that has most directly affected how Americans think about themselves and their world. Arguably, Tomorrowland and Adventureland are just variations on the theme of Frontierland played in a slightly different key.