This adjusts the brightness of the darkest parts of the image. Set too low, and shadows will be too dark to see. On some TVs, ...
If your devices only support up to 4K at 60Hz, a "premium high-speed" HDMI cable (18Gbps, HDMI 2.0) is perfectly fine. Again, just avoid really old or thin cables. Early HDMI cables (HDMI 1.4 or older ...