And you're going to base this quota on which Country's population ratios? The US?
Quotas for representation? You mean racially and ethnically? If I had control of Star Trek, amongst the Human population, I would have it be reflective of the actual distribution of people of our world, not the United States. White people would be a minority because that's what they are on Earth. I suppose if I were going to get real nitty gritty, there'd be a lot more Singhs and Wangs than Smiths and Johnsons.
If you mean in terms of sex/gender, I think there is probably no real difference across countries. Just because Americans' LGBTQ+ people are more open and out, I don't think it means we have a proportionately larger population of them than Malaysia, Pakistan, Eswatini, or Uruguay.
Outside of human diversity, Starfleet seems overwhelmingly dominated by our species. I'd probably address that issue more broadly, by either highlighting why Starfleet is less attractive to non-humans, or why are the crews so segregated, and if that is the case, why are the human-dominated ones still the most prominent?