HDMI 2.1 is useless if the image is processed. Those 48Gbps are used to transfer a 4k signal full RGB 12bit @120Hz and to preserve the image quality and at the moment the image is with "blur"/resolution downscale, so the image is not 1:1 like on the input.The key attribute of HDMI 2.1 support is Enhanced mode with 4K120p with full bandwidth 48Gbps support for uncompressed audio formats. Enhanced DV was added as a separate mode because it won't work at that framerate and Sony also added standard TV-led Dolby Vision capability.
Enhanced DV should work in [email protected] at full 48Gbps, but I think there are other limitations like VRR, ALLM, the processing power of the CPU and the "blur"/resolution downscale.