I guess Ireland is part of PESCO?

https://pesco.europa.eu/

Specifically, joining NATO would require the ROI to come to the defense of the UK.

For previous generations of politicians, that was unthinkable. De Valeera refused to join WWII even after Churchill offered him NI in return.

Also think of it strategically. Imagine the UK was invaded (Russians, Nazis, whatever). There’s a chance the government would have to abandon England, Wales, and Scotland, and relocate to Stormount.

That would put the ROI in a tough spot. But that spot would be a lot less tougher if they were strictly neutral.

The current Irish policy was created when the threat of a Nazi invasion was very real.

It’s worth pointing out UK fighter jets regularly intercept Russian interlopers over Irish skies.

Which Ireland are we talking about?

There is only one state named Ireland. And it's not "Republic of Ireland" either. That is a disambiguation, not the official name of the state.

The one that's not part of Nato?