We regret but have to temporary suspend the shipments to USA

> otherwise they assume the entire PCB consists of copper, aluminum, and steel, and charge a 100% tariff on the whole product.

Do I understand this correctly that if I have a 1kg product that costs $1000... the US is trying to charge me a $1000 tariff on at most $10 [1] worth of metal?

[1] Copper is the most expensive of those metals at roughly $10/kg

If you don't go through the work of detailing your materials, then yes, they have to assume worse case as they are not going to go through each package individually and compute an accurate number for you.

I wonder who will flinch first. I highly doubt domestic manufacturing can scale up fast enough to meet demand but It'd be fun to be proven wrong.

You're assuming domestic manufacturing will scale up... tariffing the raw inputs to manufacturing seems unlikely to do this.