The relations between EU and UK are getting dangerously acrimonious because of a combination of factors -
1. Britain chose to leave the EU. It is only natural for the EU to feel upset. Nobody likes being dumped.
2. Britain wanted to keep the benefits of EU membership, without the cost and responsibilities. It is understandable that the EU wouldn't accept this cherrypicking.
3. Britain failed to realise that the UK and RoI must be either both in, or both out of, the EU. Otherwise, there has to be a customs border.
4. This customs border can either be at Newry and all along the NI/RoI border - clearly contrary to the Good Friday Agreement - or in the Irish Sea - which understandably upsets the good folk of NI who don't all want to be treated as different from the rest of the UK. So, unless the British want to go back to the days of the Troubles, or alternatively eventually lose NI to a reunified Ireland, the only way they can have Brexit is to persuade Dublin that the RoI should also leave the EU. Not much chance of that! In all reality, Brexit just isn't practicable. Cameron is not a stupid man; he surely realised that before calling that referendum?
5. Having insisted on completing Brexit, despite many opportunities to think again in the light of facts becoming increasingly obvious, the British are so so surprised to find that they can't trade as freely as before. But it can't possibly be their fault!
6. The EU handled Covid vaccination poorly, and are way behind Britain on getting people immunised. Britain got that more or less right. The EU doesn't like to admit that, and accuses Britain of hogging the available vaccine. Very foolishly, the EU threatens to interrupt trade between NI and RoI because it thinks Britain will use this loophole to hog more vaccine. But understandably, when Britain has in the past threatened to breach its treaty obligations.
So, lets be grown up about this. Covid is everybody's problem and UK and EU should try to be better neighbours. Better still, Britain should swallow its foolish pride and admit that Brexit doesn't work, can we come back?