Iirc, one of the biggest issues is the difference in gravity you experience across your body. If the difference is too great, people get nauseous. That puts as lower limit on how small the ring can be. When the ring gets big enough, it’s moving too quickly for walking the opposite way to be an issue. Assuming you’re planning everything around 1g.

The EU has no ability to create regulations in other countries. I assume they hope that increasing the cost of business will convince manufacturers in other countries it is financially “worth it” to invest in cleaner manufacturing.