I created a local (email + password) account in my Azure AD B2C tenant, which successfully signs into my web application via user flows. However, this account cannot access or modify B2C components such as user flows or policies. Can a local B2C account be granted administrative permissions to manage B2C settings? If not, what is the recommended approach for managing B2C configuration while also being able to test the login experience in the web app?
No, it's not possible.
Even though the users that log in through policies and user flows are in the same user list in Azure Portal, they are not the same as the Entra ID users used for administration.
You need two different users for these tasks. One that can log in through user flows/policies and another that has admin roles in the AAD B2C tenant.