1. Removal of de minimis / low-value duty free exemption. Plenty of countries have very low thresholds to start collecting sales tax on imports. A moot point as a lot of platforms (Etsy/Amazon/Ebay/Aliexpress/Temu) charge the destination's US/EU/Aus sales taxes already. Usually a higher threshold to start collecting duty. Duty is much more cognitively difficult to assess. Historically, sales taxes were more than duty for most items anyway. US is now another exception here.
2. US not accepting "duty-unpaid" postal shipments. This is VERY unusual.
As of today, I can walk into the post office and send a parcel to any country in the world. The destination customs will figure out if/what duty/taxes are owed and collect it from the recipient. I don't need to know, nor care, what the rates are in Zimbabwe, Pakistan, Colombia or San Marino. The buyer should know and can complain to their gov if it's unreasonable/incorrect.
Next month, USA will be the sole exception to that. Air freight to USA is going to get a lot cheaper if anyone is looking.