We don't have B2C specific documentation for Outsystems integration and you would need to configure a custom solution.
We do have a guide for outsystems integration with regular Microsoft Entra ID.
https://learn.microsoft.com/EN-US/entra/identity/saas-apps/outsystems-tutorial
That said, you can refer to the OIDC Oauth user flow guide to see how to configure your B2C connection.
OAuth 2.0 implicit grant flow - The Microsoft identity platform | Microsoft Docs