Shipments under $800 that are sent through the international postal network will be “subject to a duty rate of either 30% of their value or $25 per item (increasing to $50 per item after June 1, 2025).”
That’s the end of cheap treats from AliExpress, Shein and Temu, I guess. 
USPS scanners now have message reminding us to “collect duties” from packages.
Most likely will mean that carriers will leave Peach Slips in a customers mail box or door telling them to come to “Post Office located at X address” to pay the duty. Not many customers are comfortable with the idea of the mail carrier knocking on their front door and asking for money before handing over packages.
That’s assuming that the carriers don’t just ignore the message/find a way to bypass the request in the scanner.