Guide yourself by the commits.
Zustand was placed from a new branch, before that it was the redux studies.
It was a simple structure study about the Redux, so nothing complex.
The structure of folders always can (and probably will) change from project to project in companies... the last I worked, each folder with your functionalities had its own reducer, actions, constants, selectors and saga if you may, others was more like this project but in a bigger scale ofc.
Some didn't use Redux Thunks, only Redux Saga, so adapt yourself and study those two topics.
Zustand in here is using version 4, but I notices that it's in version 5... and it had some major updates from this project... but you can follow some part of the documentation, it will help.
I worked in a company that instead of having one big store, we had divided, like usePreferencesStore, useOrganizationStore, useUserStore, etc., in different files, I prefer this way.