https://wccftech.com/xbox-series-s-x-are-the-only-next-gen-consoles-featuring-the-full-amd-rdna-2-architecture-says-microsoft/

Immediately following the hotly anticipated AMD RDNA 2 'Big Navi' Radeon RX 6800 & RX 6900 reveal event, Microsoft published a blog post on Xbox Wire penned by Technical Fellow Andrew Goossen and Director of Program Management Jason Ronald. The article congratulates AMD on the unveiling, but also makes a point to highlight on the Xbox Series S and X consoles are the only next-gen ones featuring the full support for AMD's RDNA 2 architecture.

We here at Team Xbox would like to congratulate and celebrate our amazing partners at AMD on today’s announcement of the Radeon RX 6000 Series of RDNA 2 GPUs. [...] The long-term strategic relationship between Xbox and AMD over the past 15 years, beginning with the Xbox 360, is at the heart of the Xbox Series X and Xbox Series S. With the upcoming launch of the Xbox Series X|S on November 10, together we are ushering in the next generation of gaming delivering a level of power, performance and compatibility never before seen in console gaming, powered by AMD’s latest “Zen 2” and RDNA 2 architectures.