Reminds me of Dynamics Customer Service where you set the holidays in the admin section.
Simple method, create an array in the Flow of the holiday dates (if you have it in the company somewhere can probably import into the array via a text editor).
Every time the flow runs, just do a quick if current date is in the array then abort.
This holiday calendar should perhaps be a SharePoint list / DataVerse entity where the dates can be stored if you want it done more nicely.
