Who should set the rules? If you should follow national rules in importing country, would not this mean that most European countries would have to ban products from USA?

Well, yeah, that's the idea. If Europeans want to maintain some standards, it doesn't make sense that companies can simply relocate abroad to escape enforcement.

On the other hand, if a company would want to sell to EU, it would simply certify/prove that its supply chain follows the standards!

Since hn don't show who upvote you, I'll add a small comment that I hope EU and others would dare to do more with this than they do now

I like that, call it a fix for the problem of the common good. About time we recognize the entire planet is our home and if someone trashes part x it eventually spreads to part y.