Europe buys plenty of stuff from countries outside the EU. Agreed they won't buy stuff that doesn't comply with their regs - that's fine. If they don't want to buy some stuff no one is forcing them to do that.Because to sell in to Europe we have to produce goods that comply with European rules and regs.
No barriers between Northern Ireland and the Republic means free movement of people.
What's hard to understand?
There has been free movement of people across the Irish border before the EU even became a thing. Let me remind you once again that the UK has repeatedly promised that it will install no hard Irish border post Brexit. You don't seem to understand this. You keep responding as if the UK had said that it does intend to install such a hard border.