I must have missed this, please explain....
You've missed lots of it, though "missed" is being generous given that you've probably ignored all of it.
For a start, the deal in effect
permanently puts the North in the EU customs area (rather than May's deal, which put us all in a temporary customs area); under this if goods go from Liverpool to Belfast and they are "at risk" of going to Dublin or any other part of the EU, customs duties must be paid. This will mean that everything will have custom duties paid on it (indeed the deal assumes this when it says that the UK will be responsible for refunding anything that duties are paid incorrectly). There will almost certainly be EU officials (probably from the Republic) at ports of entry into NI to make sure duties rules are followed as well - the deal gives them that right.
Standards of goods will also follow EU rules rather than the UK's in NI, which will - combined with Johnson's wish to lower our standards - mean that goods standards here will probably quickly become a lot different than they are there, which will mean they get their goods from there rather than here because "ours" will not be legal there.
What will exacerbate a lot of this will be the economic effect of the deal on the mainland UK - which is going to be considerable (though less than no deal), and the humiliation that Unionists will suffer by being so blatantly screwed by this. Sooner or later someone is going to suggest that the North needs closer ties to the EU rather than the UK, and a majority of the NI population will agree with it.