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Heating water causes water to expand in volume. The hotter the water, the more expansion, and the higher the pressure.
When thermostat is set to 120°F, then there is less pressure than a tank that is heated to 140°F. \
However, even 120°F can easily cause pressure that exceeds safe working limit of 150 psi.
Normally excess pressure is not a problem because it expands back out the cold water line and into the city's water main -or- into the pressure tank of water well ... where the pressure is absorbed and mitigated by the pressure controls that are required for the water supply.
Heating water becomes a pressure problem when heated water is blocked from expanding back into cold water line, createing what is called a closed system. Resource: closed system. Blockage can be caused by a check valve, pressure reducing valve, shut off valve or other obstruction in the cold water line.
Result: TP will drizzle out water whenever tank is heating.
Typically a pressure problem caused by closed system is solved by installing correctly sized expansion tank. Resource:  Read about expansion tank
High pressure can also be caused by the city or municipal water supply, often resulting in 100+ psi that causes TP valve to release short spurts of water, especially when water heater is heating.
Ideal water pressure is 40-60 psi. Use a pressure gauge on water heater drain valve and compare with outdoor spigot. Compare household pressure with nearby homes. Buy: pressure gauge
According to water heater manufacturers, the maximum pressure for home is 80 psi. Why? Anything over 80 psi risks TP releasing water, and shortened life of plumbing installation. If pressure is over 80 psi, then a pressure reducing valve is installed, along with an expansion tank Resource: expansion tank
Rural water wells have a pressure switch that can be dialed down to 40-60 psi using small wrench. Replace pressure switch if pressure cannot be controlled.Resource: TP leaking lots of hot water

Residential gas water heater has an ECO (energy cut off or high limit). The ECO trips when water inside tank reaches 180-188°F, sometimes requiring gas valve replacement. More recent versions of electronic gas valves generally come with reset protocol when ECO trips. Resource Troubleshoot gas valve

Residential electric water heaters have a red reset button or ECO that is located on upper thermostat. The ECO trips at 170-180°F +/-5°, shutting down electric power to elements. With electric water heaters, no damage occurs to thermostat because of ECO trip.

If the ECO malfunctions on either gas or electric heaters, or something else happens to cause runaway heating, the TP will release the high temperature water, saving integrity of heater and preventing steam explosion.

''If the temperature probe on the T&P of a residential water heater senses water temperatures of  210° F, the valve will stay open until the temperature probe cools."
The probe is at top of heater ... but cold water enters the bottom of the tank ... so it may take quite a while for the probe to cool. Result: you will have a large volume of water discharging out the TP before the temperature probe cools.
Because super heated hot water is dangerous and can cause considerable property damage, it is best to have adequate floor drain, or route TP overflow tube to outside, or into a drip pan that has a drain line leading to outdoor or to an open drain etc. In this instance, do not expect a small metal can to catch the full volume of overflow.