That’s one metric but it’s not enough to answer the question and misleading in key ways. Average GDP is not the same as the average person’s income, and you can’t say whether that’s good or bad without also looking at the cost of living. If your income is not going up at the same rate as your expenses that positive trend turns out to be a mirage and that’s where much of the reported pain for Brexit has been since introducing trade barriers makes goods and services more expensive.
Some trade barriers have also been lowered since Brexit, reducing costs - e.g. EU protectionist tariffs and quotas on things such as oranges and rice which reduces the cost of living.
The effects of Brexit are tiny compared to the lingering effects of Covid, and the increase in global prices caused by the invasion of Ukraine.
