This customer account feature prevents guests from shopping at your store.
Only account holders that are signed in are able to view products and place orders.
Use this feature to sell your products to a specific group of customers.
You can set up this feature in [Themes (PC) > Features > Splash page] in the admin page.
Once you activate the splash page and change the option to [Only for customer accounts], only customer account holders will be able to access your store.
Refer to the guidelines for further information.