"Business casual (European standards), which means long trousers or pants, shirt, jacket, with or without tie (no t-shirts, no polo, no jeans, no sports shoes or sneakers or slippers, no hats or caps (except for religious reasons) and the equivalent style of dress for women players.

National costumes and team uniforms are allowed."

It quite literally says "European standards."

National costumes -- I don't know the context here -- usually means vetted traditional clothing (such as, for India, a sari, but not the much more common selwar suit). It also -- by definition -- excludes minority groups (for example, Inner Mongolia or Tibet in China, or the Kurds in Turkey). There's also the very practical matter that "minority groups" include neurodiversity too.

The whole point is to judge people on their chess and not on their looks. It's the exact same issue as professional hairstyles or, before that, professional skin colors. A 1930-era US or German management consulting firm would obviously look worse to clients with a non-white consultant. There was an objective reason to discriminate in positions. That didn't make it right.

In either case, if the goal of FIDE was to make money, discriminating would make complete business sense, regardless of ethical value.

If the goal is to promote chess, people should be able to see themselves in the game, and participate regardless of how they choose to look. Back to the management consulting example, in 1930, a qualified black management consultant would serve the additional benefit of being an ambassador to and role model for their community.

So a USA player can wear blue jeans?