Trade is bi-lateral. The UK’s trading partners were also harmed by their decision to leave. Short term, it’s just simply a net negative for everybody. Long term (decades), the UK will have a long run growth rate lower than the rest of the EU. Granted, our lack of a crystal ball means that we can just debate outcomes ad nauseum.
If I recall correctly, the UK changed the way in which they compute the government contribution to GDP (going from G being just cost to some estimate of the output). This caused both the COVID drop and recovery to look steeper.
The UK was the hardest hit by COVID, but it has recovered well.