For the countries with no New Year's, I found two solutions. Using Unique and using Summarize with concatenate. The later option was the one for best practice for me, because Unique relies on the date, which shouldn't be the case if we want to investigate other festivities.
My solution in preparation for Alteryx Foundation Micro-Credential Exam. Solved all of the Weekly Challenges from "Alteryx Foundation Micro-Credential Exam Prep Guide". Loading all of them together.