I've been living in Brussels for a few years now, and during this time met quite some people in the EU bubble.

The majority of them seem to come from the same regions, studied at the same universities, move through the same internships and institutions, go to the same spots for holidays, hang out and party at the same places (Plux), and the most shocking one is, almost exclusively, date and marry other members of the EU bubble.
Talking with them, I start to notice more and more of those patterns. They clearly don’t come from humble backgrounds, and many seem pretty disconnected from the average reality of the countries they come from

So my question is: at what point does a professional elite become something closer to an elite caste or even a new aristocracy? Am I overreacting to a normal professional bubble, or is Brussels genuinely helping create a socially closed ruling class at the EU level?

It's an interesting hypothesis and very probably not entirely devoid of any merits.

I see this is your first post, so tell us a bit more about yourself if you feel inclined. Where are you from, what is it you do in Brussels, etc.?

It may be that interest from UK citizens in what happens in the EU is on the wane, given that the UK opted, in 2016, to leave the EU, negotiated their withdrawal subsequent to that and embarked on a new trading etc relationship effective as of 1st Jan 2021.

What is it that drew you to post on that topic on this forum, which is primarily frequented by UK citizens resident anywhere in the world outside the UK?

Ref. your para re interest from British citizens. Another IB forum I subscribe to has British residents (on both sides of the argument) constantly banging on about the EU! Much to my annoyance!

And I'm not referring to recent chatter about Starmer's efforts!