John, you're right... It is getting increasingly difficult to get small packages, particularly "commercial" ones, in and out of the UK. Bad enough that many small UK sellers of individual items have for years been unwilling to dispatch an item to an address outside the UK -
This item cannot be dispatched to your address... etc - even when there is no 'sales territory' to be respected. Could be a bit of classic British "Fog in Channel, Continent Isolated", but I suspect just sheer laziness on the part of many sellers who could not be bothered with the previous utterly straightforward business of sending a parcel to anywhere in the EU (or indeed anywhere) from their local proper Post Office.
Anyway, Brexit has now screwed things up properly. I recently placed an order with Chevronics UK for two items, delivery to here in Spain, total £76 plus postage. Chevronics, correctly now, did not add VAT, and the parcel arrived a couple of weeks later courtesy of Correos here
and FedEx. FedEx?? FedEx had been handed the package by Correos, whose customs office had calculated the VAT due - on the goods, the postal and courier costs,
and their own and FedEx's fees! FedEx's fee was €15 . . . for collecting the tax due . . . which they had been sub-contracted to do by Correos.
Long-and-short, I had to cough up €44 to the courier before he would leave the parcel. In the end, the all-in cost of two pairs of NOS BX mudflaps was €179

. Pre-Brexit, none of this palaver, paperwork and on-cost would have happened. Little wonder that many small sellers, and large sellers of small deliveries, have now given up.
Amazon, eBay and co have sidestepped much of this by collecting VAT (at the appropriate rate) at the point of purchase, even when packages are being sent to another country. They had no choice: millions of customers would have deserted them if faced with local tax payments, fees and paperwork. I see that the big guys in China (eg AliExpress) are now shipping small packages in bulk to their central warehouses (in our case, just outside Madrid), who then re-pack for a local postal delivery to the customer in Spain.
This chaos is now also hitting family presents sent from UK to family abroad, apparently. The odd M&S jumper, or pot of special marmalade, now attracts customs declaration paperwork and VAT documents. It will get worse before it gets better, I think.