Recognising an embassy has nothing at all to do with whether you think the entity represented is a good or a bad thing. The widely-reported and inevitable procedural snags over customs formalities etc which are hitting UK-EU trade since the Brexit transition ended on January 1st can be resolved fairly quickly, provided there are working channels of communication. And there are still a myriad of unresolved issues beyond trade which were simply parked for later negotiation at the time the trade deal was signed.
Things like this will only prolong the difficulties, utterly needlessly.
The thing is — this plays to his base as “we socked them in the eye”, while forgetting to mention that this also caused the UK to sock itself in the eye