I like the design and the way you are handling calculations.
Some edge cases to consider are:
IMO using redux on this is a bit excessive, but I get that you are trying to show it working together and I would think recruiters would understand that too.
One potential thing I think could be refactored is having a seperate function and button typed out for each number. Right now there’s a whole lot of code handling the numbers 1-9 that is repetitive. I would consider refactoring to create the jsx buttons in a loop and possibly trying to have one function to handle the numbers.
Keep up the good work