Without diving into the ins-and-outs of this, my current contract contains a claim like this. Well outside the US, and the UK/EU - it's in South East Asia.

It says something like "on company equipment" and/or "reasonably related to skills/knowledge gained or applicable during employment with the company".

So I wouldn't quite quote this as being US imperialism. I seem to recall similar clauses in my previous contracts, but can't swear on it.

My take is the "skills/knowledge gained or applicable with the company bit": if its in my company's core market, then sure. If it's from training they paid for/provided (say - I don't know - Kotlin, if I didn't already know Kotlin) then OK.

But if I make a PHP/JS app, in my own time, in an unrelated market, then they can bite me for it. Obviously, in a more litigious environment, some people may not want to take that risk.