Per https://help.shopify.com/en/partners/dashboard/managing-stores/development-stores#the-development-store-password-page, it states that the password can only be removed once the store has been transferred or switch to a paid plan.
You can remove the password page only after you transfer the store to a merchant or switch the store to a paid plan.
However, it is still possible to remove the password by using the GraphQL PreferencesSave operation.
passwordProtection.enabled
property to false
The store is now paswordless.
āāāā
Disable development store password