I have followed the instructions on this page to add the ability to sign up / log in to my application using a Microsoft Account. Personal accounts seem to work fine, but organizational IDs do not. And if I type in an email address that is both an organizational ID as well as a personal account, at no point am I prompted to choose "Work or school account" vs. "Personal account". When I use the same email to log into Azure, I am prompted to pick one.
The configuration instructions talk specifically about enabling "Accounts in any organizational directory and personal Microsoft accounts (e.g. Skype, Xbox, Outlook.com)." and I have confirmed that this option is set properly in my registered application.
Is there something else I need to do to enable sign up and log in with organizational IDs in my AADB2C application?
Although you registered an app with the type is Accounts in any organizational directory and personal Microsoft accounts (e.g. Skype, Xbox, Outlook.com), it doesn't mean you have enabled sign-in for users from an Azure Active Directory (Azure AD) organization.
The configuration in this article is only for MSA. You define the account as a claims provider that Azure AD B2C can communicate with through an endpoint by adding a claims provider.
If you want to enable sign-in for Azure AD users, you should define Azure AD as a claims provider.
You should finish the configuration on this page.