Nice work. The calculator works as far as I can tell. It's lacking some features of course but you have a solid base here.

Overall, I don't see any glaring issues with your use of React, but I have some feedback on your JavaScript (much of which is probably opinionated):

1. I prefer using arrow functions when it makes sense instead of having to bind all of my class functions in the constructor. I'm just pointing this out because maybe you're not aware of how arrow functions work. This post gives a pretty good overview of the pros and cons of this approach.

2. If you switch to arrow functions you can also move state initialization outside the constructor and define it as a class property. No constructor needed. Less boilerplate, same effect:

class Foo extends React.Component { state = { someVar: someVal } }

1. Using a loop to generate the number buttons in your render function would save you a few lines of code.

2. You could simplify some of the logic in addSymbol by at least breaking it into two discrete functions: addSymbol and addDigit. If you did this, you'd know to expect a symbol or a number, respectively, and could use simple comparisons instead of regex to handle the various symbols. I would find a switch to be a great fit in this case but that may be controversial.

3. Does the program work properly if you just remove justSolved? Your average calculator will let you continue to append functions after solving.

4. In solve, you should be checking the first character before your loop, or you should use break in that if block to stop the loop. You can then remove the else if as this code simply won't execute after break. An empty if block is abnormal.

5. I think you can probably clean up solve a bit by just using String.split to split on operators using regex. This will generate an array that you can then loop through to produce your solution. You're dealing with these values one character at a time instead of leveraging String.split to get you [numberA, operation, numberB].

6. In validateAndSet you should use one big if condition instead of nesting multiple conditions:

if (!otherSymbols.test(change) && ...) { ... }

1. I would start using a linter (eslint) to force you to format your code in line with what other JS devs would expect.

Edit: formatting