There is no official announcement, codename "Xbox 720," or credible leak regarding a successor to the Xbox Series X|S (launched November 2020).
Microsoft typically keeps hardware roadmaps under tight wraps until 12–18 months before launch. Given the current generation's mid-cycle refreshes (like the 1 TB digital Series X and white Series S), a brand-new generation is unlikely before late 2026 at the earliest.
For now, the Series X|S remains the focus, with backward compatibility ensuring your library carries forward.