There is no answer to the Northern Ireland question.
Up to a point.
The Irish work on "de-dramatizing" the border issue has highlighted that the only checks that MUST be at the border are phytosanitary ie animal and food checks. All other can be performed away from the border.
If "no hard border" means only no physical checks at the border, then an All-Ireland approach to agriculture removes checks on the North-South border, and introduces no new regulatory checks on the East-West border.
It would require NI to accept Single Market rules for agriculture and the EU to accept NI agriculture inside the Single Market.
However given the fallout from Salzburg, I can't see any agreement being reached.