That is a huge drop in a 6 year period. The times they are a changing.
From the Irish Times
https://www.irishtimes.com/ireland/2023/05/30/census-2022-results-all-the-data-on-irelands-latest-demographics-as-it-happens/
The proportion of the population who identified Roman Catholic as their religion fell from 79% in 2016 to 69% in 2022.
There was a fall in the proportion of the population who identified as Roman Catholic from 3,696,644 (79%) in 2016 to 3,515,861 (69%) in 2022. The No Religion category increased from 451,941 people to 736,210. The Church of Ireland category showed little change but remained the second largest religious category with 124,749 people (2%).