Is Guy Fawkes Day in November not a big thing in NI? It is in England, at least. Although the traditional burning of the effigy of Catholic dissident/terrorist Guy Fawkes is becoming less common and people just are more commonly just treating it as a general holiday.
No, we don't observe it at all, in either community. Halloween is bigger here, and observed by both main communities, it's probably close enough to 5th November that we've just ended up forgetting about Guy Fawkes.
Plus it's taught in school as an English event, and we have enough of our own history going on in the early 1600s.
Closest I can think of is the 12th July, which is a holiday, but not one celebrating burning Catholics[0]. You might be referring to the bonfires that are lit on the 11th, but that's not a holiday.
Aside from some small events in Scotland, the 12th July is not celebrated in the rest of the UK.
[0] https://en.wikipedia.org/wiki/The_Twelfth