You’re not forfeiting any rights by buying something on Aliexpress.
US law doesn’t apply in China. Nobody is going to take your case because some Aliexpress seller has no reason to even respond to your threats to take them to court.
You're not legally forfeiting rights as in the laws saying "you lose these rights", but in common parlance of course you are as you explain in your second paragraph.
If the default situation is that when you buy faulty goods you have legal recourse against the seller, but when you buy direct from a foreign country you do so knowing that should there be a problem you won't have that option, you are de facto forgoing, or forfeiting, those rights by choosing to make that purchase.
It's nothing specifically to do with China, but it's how things work (except/until between countries who agree to mutual protection of consumers rights, which I think is the case between EU member states but I'm not sure about any other examples).
US law doesn’t apply in China. Nobody is going to take your case because some Aliexpress seller has no reason to even respond to your threats to take them to court.