Anyone can help me to interpret the Supply Voltage vs Temperature from this datasheet ? What does it mean ? Why the supply voltage modifies ?
It's a standard derating curve.
The Hall element requires a current to be passed through it, and this will be fed by a regulator in the device. It's most likely a linear regulator, so it produces some heat that is proportional to the difference between the voltage across the Hall element (probably fairly low) and the supply voltage. To allow for the temperature differential between the chip and outside world, and to keep the chip temperature below its maximum, the allowable power dissipation must come down as the ambient approaches the maximum - meaning that the maximum allowable supply voltage must come down - the current through the element is regulated so that its sensitivity remains constant.
Note that these sensors are specified to operate at a higher temperature (150C) than most semiconductor devices. The limitation is that the power they dissipate must be limited at temperatures over 125C to avoid thermal problems. To limit that dissipation at higher temperatures, the manufacturer specifies a lower maximum supply voltage. That is the purpose of the Supply Voltage vs Temperature curve: to warn the user not to exceed the plotted supply voltage if the device will be subject to temperatures above 125C.