At what temperatures in Fahrenheit, Celsius and Kelvin would a human body freeze near instantaneously?

Minus 40 is the temperature on both the Fahrenheit and Celsius scales where exposing any skin to the cold is no longer safe. At this air temperature, or its windchill equivalent, skin can freeze almost instantly. On the Kelvin scale this would be approximately - 233.20

At a temperature of minus 28oC (minus 18oF), flesh will freeze in 15 minutes or less.

https://mississaugaautoloan.com/qa/what-temperature-do-humans-freeze-instantly.html

According to this site, it is the core body temperature that matters. If it is below 35 degrees C or 95 degrees F, problems will occur. Many people in the Arctic live perfectly well in a temperature of below -40 degrees C.

http://www.madsci.org/posts/archives/2001-02/982593090.An.r.html

There is no precise core temperature at which the human body perishes from cold. At Dachau's cold-water immersion baths, Nazi doctors calculated death to arrive at around 77 degrees Fahrenheit. The lowest recorded core temperature in a surviving adult is 60.8 degrees. For a child it's lower: In 1994, a two-year-old girl in Saskatchewan wandered out of her house into a minus-40 night. She was found near her doorstep the next morning, limbs frozen solid, her core temperature 57 degrees. She lived.

https://www.cbc.ca/news/canada/saskatchewan/15-years-later-toddler-who-survived-freezing-leads-normal-teenage-life-1.838801

The fact that the body is possible to survive under such conditions is due to thermoregulation.

Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when temperature surrounding is very different. This process is one aspect of homeostasis: a dynamic state of stability between an animal's internal environment and its external environment (the study of such processes in zoology has been called ecophysiology or physiological ecology). If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as hyperthermia occurs. The opposite condition, when body temperature decreases below normal levels, is known as hypothermia.

https://en.wikipedia.org/wiki/Thermoregulation

These are some symptoms that will occur when your core body temperature is below 35oC. (Hypothermia).

Normal body temperature in humans is 37 °C (98.6 °F). Hypothermia can be divided in three stages of severity.
In stage 1, body temperature drops by 1-2°C below normal temperature (1.8-3.6°F). Mild to strong shivering occurs. The victim is unable to perform complex tasks with the hands; the hands become numb. Blood vessels in the outer extremities constrict, lessening heat loss to the outside air. Breathing becomes quick and shallow. Goose bumps form, raising body hair on end in an attempt to create an insulating layer of air around the body (which is of limited use in humans due to lack of sufficient hair, but useful in other species). Often, a person will experience a warm sensation, as if they have recovered, but they are in fact heading into Stage 2. Another test to see if the person is entering stage 2 is if they are unable to touch their thumb with their little finger; this is the first stage of muscles not working.
In stage 2, body temperature drops by 2-4°C (3.6-7.2°F). Shivering becomes more violent. Muscle mis-coordination becomes apparent. Movements are slow and labored, accompanied by a stumbling pace and mild confusion, although the victim may appear alert. Surface blood vessels contract further as the body focuses its remaining resources on keeping the vital organs warm. The victim becomes pale. Lips, ears, fingers and toes may become blue.
In stage 3, body temperature drops below approximately 32 °C (89.6 °F). Shivering usually stops. Difficulty speaking, sluggish thinking, and amnesia start to appear; inability to use hands and stumbling are also usually present. Cellular metabolic processes shut down. Below 30 °C (86.0 °F), the exposed skin becomes blue and puffy, muscle coordination becomes very poor, walking becomes almost impossible, and the victim exhibits incoherent/irrational behavior including terminal burrowing or even a stupor. Pulse and respiration rates decrease significantly but fast heart rates (ventricular tachycardia, atrial fibrillation) can occur. Major organs fail. Clinical death occurs. Because of decreased cellular activity in stage 3 hypothermia, the body will actually take longer to undergo brain death.

https://en.wikipedia.org/wiki/Hypothermia

I don't know the answer to your question, but I know nobody's come close yet, not if you mean the entire human body freezing solid, which, of course, would vary greatly depending on the size of the body, and presuming you mean stark naked.

Frostbite can happen very fast at -20 F. or less, but I can tell you from experience I've never suffered frostbite despite many brief--say, three to five minutes--exposures of bare skin at the temperature.

The thought of a human being instantly frozen solid boggles my imagination. Sorry to be gross, but at -40 F. I've never even gotten my spit to freeze before hitting the ground although some claim this happens at -30 F. They must be taller than I am!

"Instantaneously" is poor "terminology". This "instant freeze" would occur only in the movies. A Sci-Fi/Horror flick.

Density and total mass would determine the freeze rate.

Matter enjoys holding on to heat even though all "natural state" is absolute zero.

It all comes back to Stars.