Brexit might have had an impact but it’s one of 10 things badly wrong with europe as a whole.
Even if you look at it as a purely engineering problem you'd see that adding more red tape on trade would be most detrimental to the smallest player. In the relationship with the EU, the UK is the smaller player.
Now, what about the other “major powers” which are “predicted” to grow their economy? France’s GDP per capita has peaked in 2008, and never recovered since then. Italy? Same. Spain? Same. Belgium? Only recovered to 2008’s figure in 2021, same as Netherlands, Denmark, Finland. Sweden also only now recently recovered to its peak in 2011.
In fact, the only major EU economies that did not simply recover to their 2008-2011 peaks, but rather grown beyond them, are Germany, Poland and Czechia.
The truth of the matter is that EU economies are deeply stagnant, this is by no means a UK specific problem. There is no reason to predict growth in EU but not in UK.
https://countryeconomy.com/gdp/germany
Germany growth:
2022Q4: -0.2%
2022Q3: 0.5%
This is economically illiterate, calling it an engineering problem doesn't change that.
Trade happens when both sides can benefit. If trade stops happening, both sides lose. Artificial trade barriers do not mean one side "wins", they are always and everywhere a way to penalize some local citizens in order to prioritize others, usually owners of businesses that are favoured by the state in some way.
At any rate it's an academic question. UK exports to the EU recovered to the prior level, it is selling the same quantity as before. Imports are lower, so UK buys less from the EU. Balance of trade therefore actually improved. This is not widely reported because the media is full of people who want everyone to believe Brexit has been an economic disaster. The reality is it'll never be possible to know because any impact is so small as to be invisible against the chaos caused by lockdowns.
"It Was The Fu*king Banks" - YouTube https://www.youtube.com/watch?v=GtWA3jQN1Pg
Brexit and the backlash against globalism is a result of the economic malaise brought about by those policies, not the cause of that malaise.
Heck, if you look at the chart of GDP per capita you can’t even tell where the Brexit vote happened or when Brexit formally happened. Something similar happened Italy around the same time, as well as Greece.