There was approx a 10% reduction in EU trade from 2016 to 2019, largely because European supply chains began reconfiguring to exclude the UK in anticipation of higher trade barriers, which proved to be case. No such adjustment was necessary for non EU trade as the basis for this was not impacted by Brexit.
The final figure for the loss in trade with the EU is yet to be determined, but there will be a further reduction on top of the 10% reduction because when you put up trade barriers, you reduce trade and erode the competitiveness of UK businesses in relation to their European counterparts when it comes to EU trade. In other news, water is wet, etc.
Finally, we have compounded this economic disadvantage by allowing EU firms to flog stuff into the UK without the trade barriers our companies face exporting to the EU, which, I am sure you will agree, is simultaneously stupid and hilarious in equal measure.