Before some products can legally be sold into their own domestic market, British manufacturers in the relevant industries will have to submit detailed evidence and perhaps visit an authority located in an EU member state to obtain a CE mark confirming compliance with rules the UK has no influence over.
It's mind boggling how much of a disaster Brexit is and how it's just not being talked about by any senior politician.
Brexit has made life massively more burdensome for our exporters who face border checks while at the same time given EU based exporters the green light to export what they want to us without any checks at all. No wonder people say the UK has placed sanctions on itself. The EU probably had to contain their disbelief at the shitty deal Johnson agreed to.