Northern Ireland is sitting pretty at the moment - it effectively has the advantages of EU membership even though it's politically aligned with the UK.
The people yelling about it are hardline British nationalists who are horrified that their statelet isn't suffering the same problems as Britain. And of course Boris Johnson seizes on their protests, which are a wonderful distraction from the real hardship being suffered in Britain.
The EU will undoubtedly loosen some of the health rules on the inspection of goods coming into Northern Ireland; this is not a good thing, in fact. But even doing this will not stop the Unionist yells; they are offended by any difference in Northern Irish and British law. (Except, of course, in cases such as abortion rights, which they keep determinedly Texan, unlike Britain.)
For those who can't understand what's going on, Northern Ireland is the Deep South; the Republic of Ireland is California.
Unlike the early years of the Irish Free State, when Ireland was a fascist state, with suppression of women's rights, devotion to one religion, state censorship of books, films, plays and newspapers, worship of a strongman and so on.