How can I access claims for UI customization in ADB2C?

Question

I am trying to build a signin solution for a multi-tenant Web App.

I have more or less created a solution based on the B2C Multi Tenant sample provided by Marius Rochon here: https://github.com/mrochon/b2csamples/tree/3823c17def460f154e4bf4a74b2a8b8b7c14fc2e/Policies/MultiTenant

This solution relies on "Tenant Selection" in the query string, and then the backend API populates the "appTenantName" based on the query parameter.

What I would really like is a solution where, after the initial login, the user is prompted to select one of the available tenants, in a dropdown based on the "allTenants" claim (an array of strings).

Alternatively a solution where the tenant selection is based on the subdomain part of the site the user is trying to login to.

I have limited experience with the custom IEF setup, so I am uncertain if what I want is even possible.

I can see that its possible to define user input and a fixed "enumeration" for available options, but I guess I want a "dynamic" enumeration based on the claims. Is that even possible?

Or should I do custom UI content instead and load the UI from my own website (like described here: https://docs.microsoft.com/en-us/azure/active-directory-b2c/customize-ui-with-html?pivots=b2c-custom-policy