A surprise for you!
If you have to have anything sent to you by post, you will have to pay a tariff.
I had a wee shock last week, a package a friend sent me, which cost him £6, insisted on a 2nd charge of €6. The Spanish post office said it was a result of Brexit!!!
If we buy from a UK company that has done all the annoying paper work needed now we don't pay VAT in England and the company pays the Irish tax on our behalf . That rarely happens and folk are being caught out by incorrect or non-existent paper work and wind up paying two lots of VAT.
Amazon if fine for thing they sell themselves and will sort out any mistakes which are few.
I doubt any nation is forced to add a charge. It'll be a government decision, most likely. If a nation don't want custom from UK customers that's their deliberate choice. UK citizens can opt to support the UK economy/market instead, and quite right too.