The North has more restrictions on abortion than the republic has now. And you’re right - the RoI is far less Catholic.
Though I argue that the Irish troubles were less about religion and more about ethnicity - considering that the first President of Ireland was Protestant as were many of the leading lights of the movement. But they felt Irish (even if they were Anglo-Irish or Norman-Irish). Remember that Rees-Mogg is Catholic for instance, but seems the quintessential Englishman. The Ulster folks, about 30% feel British but they feel that “Britain” is leaving them, so might as well join the republic.
Oh and the Republic of Ireland and Northern Ireland jointly have a rugby team. the world is mixed up!
The population of the Republic of Ireland is increasingly made up of Poles and Nigerians. So that ethnic argument is out the window too.