The store demo notice can be enabled if your store is already online but still in construction mode. The notice will be located in the header of your store indicating that the orders will more be fulfilled in this mode.
When enabled, it will appear as a red sticky note above the header of your store saying that “This is a demo store. No orders will be fulfilled.”
Display Demo Store Notice
Determines whether the demo store notice is visible on both front-end and back-end of the website.
On the Admin sidebar, go to Content > Design > Configuration.
In the grid, find the store view that you want to configure. Then, click Edit in the Action column.
Under Other Settings, expand the HTML Head section.
Scroll down to the bottom, and set the Display Demo Store Notice to Yes.
On the Admin sidebar, tap Stores. Then under System, choose Cache Management.
Choose Flush Cache Storage.