My daughter is now studying in the UK and as a mother, of course, I am sending her nearly weekly some “stuff”, from books, to clothes, to chocolate etc.
Even me not being a UK citizen I realise that “things” changed a lot since Brexit, but really I didn’t expect, that sending anything more of 1(one) sheet of paper means spending (in my case, being not too tech savvy) over an hour on the computer, filling out forms, finding out the correct reference numbers in lists of hundreds(!) of articles and doing it all correctly, so I can (hopefully) print out the bar code to glue on the envelope. Unless I ask the people at the post office to do it and wait(!) until they have the time and find the right person, who knows how to do this and pay another 7Euros for that service.
All of this is needed and asked for by the UK rules, to receive post from out of UK!
Honestly, even before the European Union one could send a letter (with more than 1 page) and little parcels to the UK by just putting it in the envelope, get a stamp and send it.