The thing is, it’s not just Brexit that’s messed up imports and exports, it’s the pandemic too.
The ports were struggling long before the actual agreement was even signed. Part of that was because a load of people decided to do last-minute bulk importing that clogged up the ports, and part of it was due to people ordering gifts online either to avoid using the highstreet or because they actually couldn’t use the highstreet (I expect Amazon’s profits have soared this year).
Those factors were causing congestion even before the new rules came into play, so when the rules finally did come into effect it was far worse than it might have otherwise been. (It was never going to be smooth sailing of course, but events conspired nonetheless.)
(There was the 48 hour Calais border fiasco as well, but I doubt that had much effect on Arduboy imports.)
I’m not sure how much it differs (if at all), but I found this slightly easier to sift through and understand: