The 24/25th particularly is a fairly quiet time, with the vast majority of places closing as people spend time at home with their familt during this period. Restaurants that are part of a hotel are more likely to offer a Christmas Eve or Christmas Day menu, even though it is a family day in Ireland. You can find some options from the list here
Salt Hill Promenade will have some people enjoying the walk on Christmas and Boxing Day. Be sure to check out this page on day trips from Galway
as some tour companies resume service on the 26th of December.
Let me know if you have any other questions.