It isn't a loophole - this was done on purpose.

De minimis and the previous packaging regulations were used as a tariff bypass by Chinese platforms like PDD and SHEIN, which led to their crackdown over the past 24 months [0][1]

[0] - https://www.ft.com/content/067ba5bb-4da3-42fc-a57b-9dd27a8f9...

[1] - https://www.reuters.com/sustainability/eu-probes-shein-over-...

Let me spell out the loophole: Just don't use packaging. Redesign your product so it comes in a sturdy container that makes it integral part of the product itself and completely side steps the obligations here.