A common fake belief about Einstein is to think he was a theist in the usual sense. He was not. His views are closer to atheism. See https://en.m.wikipedia.org/wiki/Religious_and_philosophical_views_of_Albert_Einstein
Now, he thought there was a hidden variable because he thought the world could not be build on probabilistic processes. This is viewed by many of his colleagues as a mistake, although they all admire him for other works.
The fact that quantum mechanics is well described by probabilities does not mean that the world is badly made. It does not mean it is well made either. It is just a way of describing it that works very very well.
Trying to find a hidden variable for the sake of god is looking for what Neil degrasse tyson describes as "the god of the gaps ". It means putting god in physical things we don't understand yet. This is a pagan habit. It is like saying "there is thunder, zeus must be angry ", and looking for signs of zeus existence. It was fine, until we understood electricity, and ridiculous now that thousands of planes go over the clouds every day.
If we find such a variable, it will not be the variable of Allah swt. Just a mathematical symbol.
If we find for sure that there is no such variable (and we are having this conviction reinforced with every quantum physics experiment), it doesn't mean anything with respect to islam.
Clarification following comments : maths (mathematical objects) do not exist in the material world, only in our heads and books. For instance, a point, an object with no length whatsoever on any dimension, does not exist. When you say "this table is square" what you mean is "this table reminds me of the mathematical concept of square". Maths are a surprisingly powerful tool to describe and predict the world, but are not part of it. There is a simili debate about it among people whose area of expertise is not the foundation of maths (axiomatisation, logic, ...), but it is wrong to think maths exist (I insist a lot but I think it is necessary ).
So whether we describe quantum mechanics with stochastic mathematical objects (undeterminacy) or not is not relevant to Islam. The world we live in is not made of equations. Some equations fit it well. That is it.