If you visit the Epic Games Store and go to the section for the free games, you’ll encounter something aside from the regular free games.
The free game for the next week is not shown, instead you have an image with Christmas decorations like last year, and it’s called “Mystery Game”.
If Epic Games does the same thing as last year, that could mean that the next free game will only be available to claim for 24 hours before the next free game comes up.
If that happens, you will have to be fast, or you’ll be missing out on probably AAA games.