Every voltage regulator IC has atleast a variation of 2% or something. This can make the ADC reading way inaccurate if it fluctuates to those levels. What is a robust and common solution to this problem?
You use an external "reference". You can use anything from a few-penny LM431 to much more sophisticated references, depending on your requirements for accuracy and stability as well as noise
LM4040 is a commonly used shunt reference for moderate accuracy and low cost, but there are many others, do a parametric search based on your actual requirements. They come in two basic types- series and shunt. The series type is like a more accurate and stable type of voltage regulator, the shunt type is like a zener diode that requires some series resistance to establish a bias current.
In some cases, for the best accuracy, you may need to buffer the reference output in order to drive the ADC reference input.
There are parts made for this purpose, called voltage references rather than voltage regulators, ADR421ARZ is one such example with good noise specs.