My stance has been that in a practical sense the border is completely open.
My argument has been that it seems illogical that if the UK is supposed to have left then changes would not be manifest on the land border.
The shenanigans, as yet seemingly unresolved, regarding the 'border in the Irish Sea' point to the notion that once leaving is supposed to have happened some kind of border somewhere is established.
Recent developments have led to resistance to the notion of the Irish Sea Border (a confirmation that both the EU and the UK see 'a' border as a consequence that flows from leaving). The practical realities indicate that the 'leaving' has at the very least not fully happened, which is my point about that isn't what was voted for...a partial dogs dinner kind of leaving...the vote was simply (sic) to leave.
I don't know if you think leaving has happened in terms of all border issues being neatly sorted and agreed, but it doesn't look like that from my perspective.
It looks like a wide open bit of territory across which anything goes.
If the concept of leaving only applies to laws and paperwork and declarations and rules and such like...not practicalities, then maybe a clever lawyer can point to the paperwork and declare 'lo! The UK has left the EU', but that looks like an Emperor's New Clothes scenario, the UK has left the EU if you believe hard enough, but the practicalities are a different matter, just as you'll freeze your bollocks off in cold weather if you start to wear the same clothes as the Emperor.
Current affairs are the start of the Marching Season, and you may well find resentment about the sea border rearing its head during the time of those events.
You may well decry my references to a border as you have done above, but it is still a live issue.