For color temperature, set that according to the viewing conditions you’re in… the brighter and more well lit, the higher # is better… the darker and dimmer, the lower # is better. It controls the warmth of the whites.
For the other slider, color vibrance, depends if lcd or oled. For OLED, SRGB is the better setting. “Native” is too oversaturated, it’s the same as an oled phone’s “vivid” mode. If you like, you can give it a little bit of a boost, but you shouldn’t need to. For LCD, native is the srgb gamut compressed into the little space that the panel can handle… it will look on the paler side but the plot points are evenly spaced… and moving the slider toward boosted increases the saturation at the expense of some accuracy. Native, srgb or a little bit past srgb are all fine, but not the far end which is too saturated.
You’d be better off installing Nobara, there’s a Steamdeck version.
Install it to a SD card or something, don’t mess with the internal drive.