Interesting! Can you explain how this works? (economics noob over here)
Most of the value of an iPhone is recorded as American GDP because American IP and software went into it, Apple is keeping a lot of the price for the phone, and only sending a bit off to China for assembly (and a larger bit off to South Korea, Japan, and Taiwan for components that China is assembling). What remains is still a lot of American GDP.
A small business who is contracting China to make the thing that they then sell is also generating a lot of GDP. Yes, they send some percent off to China to make the thing, but a majority is GDP generated here in the USA (the small business does the design, marketing, sales, etc...). If they go belly up because of the trade war (very likely, since no one else can make their thing, and before China developed this capability, making the thing wasn't even possible!), that GDP is gone, the people that small business was employing are unemployed.
The increased purchases should not decrease American GDP, unless consumers are buying directly from China using Temu and are not buying at Walmart.
If you take that money you would have spent buying something in the US that has imported parts (like its assembly), and instead say go out and by a DJI drone on TEMU, yes, you've decreased GDP. If you simply have no money to buy anything because DOGE decided to cut your federal job, then that would also decrease GDP.