https://wccftech.com/amd-radeon-rx-6900-xt-lc-appears-in-online-review-navi-21-gpu-onboard/

The AMD Radeon RX 6900 XT LC is the top Radeon graphics card -- but you can only get it through an OEM or a system integrator. It is impossible to purchase alone. AMD has no intention of currently offering it for sale through any website -- even their own online store. AMD has yet to respond to any outlet as to the reasoning for not offering the GPU by itself.

However, PC Games Hardware were able to find and receive the RX 6900 XT LC. But, it was no easy task for them. PCGH purchased an entire system designed by Dubaro that included the graphics card. After receiving the system, they promptly removed the graphics card and necessary components and placed it their own system for testing.