From GoToQuiz.com, the percentages of respondents in the US who express a partisan affiliation other than Republican or Democrat:
The differences are modest (notice the y-axis begins at 20%)–but I did the digging so may as well share what I found–with the only sharp dividing line along sex. Women tend to be more conformist than men for rather obvious biological reasons. The idea that Zoomers resemble the Silents more than the generations separating the two cohorts aside, the relatively low third party–liberally defined here to include independents as well–orientation of those under 18 might just be due to a lack of familiarity with options outside the Uniparty.
Parenthetically, the survey doesn’t ask about registration or electoral intention. Even after taking that into account, though, it’s clear that a lot of people who self-identify as Green or Libertarian vote for one of the big two if they vote at all.