TL;DR: The Nintendo Switch 2 dock is expected to support HDMI 2.1, potentially enabling 4K gaming at over 60FPS when docked. It may use the RealTek RTD2175N-CG chip, supporting up to 4K 120FPS.
The Switch 2 is official ... But at the same time, Nintendo has a soft spot for dual-screen gaming as the DS, 3DS and Wii U ...