sRGB is quite literally defined as "the average 90s CRT in an office environment", i.e. full-white sRGB on a HDR display should be around 100 nits or so in those reference conditions (i.e. display set to "reasonable" brightness).

VR displays. Probably the color of the sun in linear RGB color space for rendering purpose, then converted to the display color space.

The color you will use isn't in SRGB, but is in other color spaces such as Rec2020.

Do you have a recent iPhone? Try taking a picture with the sun in it: the white of it will appear white as well, but the phone will display it considerably brighter than the white UI surrounding it.