nobody's closing borders!
Er yeah we are effectively. You’re about to discover the difference between tariff free trade and CU/SM/FOM for goods and services.
As detailed in the EU Summary and also on the U.K. gov.uk, full customs checks and procedures will still apply.
Free trade just means tariff-free (and quota-free) not customs free.
The customs procedures will include SPS checks on agriculture, customs declaration, catch certificates for fish, a load of other licenses and certs depending on the product, customs handling & clearance fees, ATA Carnets, VAT, and a whole heap of other ‘red tape’ NTBs (non tariff barriers).
The deal does include customs cooperation and simplification agreement which might help with some congestion, particularly industrial goods, but they will still all need declaration forms, scans and clearance.
The main congestion will be with lorries transporting food - live animals, meat, fish, dairy, plants, drinks, processed food, etc.
The Rules of Origin will also add to the problems. In the CU-SM we shared the same trade deals, which meant that between EU & UK we could also have customs and tariff free trade for all countries we had free trade deals with.
Now we're not in the CU-SM, the EU doesn't recognise our trade deals, so tariffs will apply to any goods traded that are 40% or more not of UK or EU origin, even if we've both got free trade deals with those countries (Japan, Canada, S Korea, Mexico, etc.)