B: Customer self-service portal: A customer self-service portal enables customers to access self-service knowledge, support resources, view the progress of their cases, and provide feedback.
Note: Based on the selected environment in Power Apps, you can create a Dataverse starter portal or a portal in an environment containing customer engagement apps (Dynamics 365 Sales, Dynamics 365 Customer Service, Dynamics 365 Field Service, Dynamics 365 Marketing, and Dynamics 365 Project Service Automation).
E: Omnichannel for Customer Service offers a suite of capabilities that extend the power of Dynamics 365 Customer Service Enterprise to enable organizations to instantly connect and engage with their customers across digital messaging channels.
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/portals/portal-templates
https://docs.microsoft.com/en-us/dynamics365/customer-service/embed-chat-widget-portal