Having probably signed such a contract, how do I find out if it is enforcable? Probably talk to a lawyer, but how do you find one that gives you a straight, but correct, answer to such a complex topic. For me it is even more complex since I'm a fake employee (contractor) in another country working for a US company.

The answer to those questions might be really unsatisfying in practice, since it breaks down to a cost calculation by the sueing company (if the company leadership is rational). So in case you get sued you have to fight defensively and bleed them enough so they give up or something.

[not legal advice]

Having talked to lawyers about this sort of case, be prepared to speak to several to find a match, or read between the lines - when you ask questions like, “If I break this clause, what sorts of liabilities am I exposing myself to, and how often in your experience does that happen?” Be prepared for, “as my client, I don’t advise you to do that.” Not super helpful in my case, as I was trying to understand the possible outcomes and likelihoods.

The best advice I got was from a business mentor which was, “if you don’t rub it in their face, they probably won’t notice, and probably won’t care.”

Which is, as you mentioned, a probability calculation.

What I would personally guess [not legal advice] is that you rate the likelihood of your employer suing higher than they do (absent anything egregious).