I think we're conflating two things. A seller has to refund / replace / repair any merchandise that is defective or not as advertised, and that's true in the US and in the EU.
A seller does not necessarily have to accept returns if you changed your mind, found the item cheaper somewhere else, or just don't like it. Pretty sure that's also the case in the EU.
That is not the case at least in the UK; you have 14 days after receiving an item, for any online purchase you make, to return it, even if you just changed your mind.
Consumer protection regulations are genuinely so nice for feeling at ease with buying stuff online.
In Brazil you have 7 days to return any online order, no questions asked. You can use the product and return if you don’t like it, provided the product is not scratched etc. Companies might try to bullshit you and say that the ToS states that they only accept returns for products that weren’t opened, but they always cave after I send them the exact part of the consumer laws that support me. They have to refund the full amount, including shipping.
Not in Europe.