Final answer:
The Microsoft Partner Network is the channel where one can get direct access to Microsoft 365 planning materials and project managers, as it is designed for professional collaborations and project management.
Step-by-step explanation:
To find Microsoft 365 planning materials and project managers, the correct channel is Microsoft's own Microsoft Partner Network (b). Although the other options provided, such as Microsoft Tech Community, Microsoft Learn, and Microsoft Developer Network (MSDN), are excellent resources for different purposes such as community discussions, learning courses, and developer tools, Microsoft Partner Network is the platform designed specifically for businesses and professionals seeking direct access to Microsoft's resources for planning and managing projects. It offers a wide range of resources including detailed planning materials, best practices, and the ability to connect directly with project managers and other professionals.