Yes, UPS and FedEx have supported customs processing for a long time, but many direct-to-consumer vendors from China are using USPS directly via China Post, which does not.

I believe there are other models now (e.g. where shipping companies bulk-import and customs clear shipments and then hand them off to USPS inside the US as domestic shipments), but the "direct parcel" USPS route going away for all formerly de-minimis-exempt parcels is still going to have a huge impact, without even considering import tariffs directly.

Advice to US international shippers: When shipping to Canada, UPS is the worst. They charge an arm and a leg to process the paperwork (often to the point where their brokerage fees outsize the actual duties and taxes owed), and even after I told them multiple times to use my own customs broker they seemed to "forget" or play games like delaying release of the needed paperwork. USPS is most reasonable, Purolator is OK, FedEx is still expensive but marginally better.