From "GCC STANDARDIZATION ORGANIZATION (GSO)'s Electric Vehicles Technical Regulation" PDF documents (thought what they're about to say is true on combustion-powered cars as well):



"All motor vehicles shall be provided with a minimum of
one rear fog lamp. The rear fog lamp is optional provided
if the intensity of the rear lamps comply with the GSO
regulation on lamps to be formulated."

I didn't fully understand the last part if I'm being honest. However, what i did notice is that around 2016-2018, a lot of cars from Asian brands suddenly began receiving rear fog light(s) as standard equipment. This is noticeable if you look at used (or wrecked ) examples of the same car between the 2016-2017 model year range or so. Previously, you only really see rear fog lights on European makes over here.

For the record, GSO is the governing body that's responsible for most regulations across the GCC nations + Yemen (with each nation having it's own regulatory take by itself). Saudi Arabia (As in SASO) in particular seems to have slight different takes on some aspects so this might not apply to them tho.