Another option I have seen used with success is to drive the user to set an option in the UserSettings menu before they can do anything else.
Your store selection seems to be a perfect fit for UserSettings. You can build one that allows the user to set or switch which store they want to operate on in the app.
BUT until they set the UserSetting, the user is not allowed to operate on anything within the app. Instead you show an Action that takes them to the UserSetting. You can lock down the app as tightly as needed, hide Actions, hide rows, hide complete views, etc until an option is selected.
The beauty is you are using built in functionality so when a user wants to change the store, they just go to the UserSettings and change it. You don’t have to build anything more.