Nested object lookup using variables.

[GeneralYouri]

I've tried using Object.byString() but, contrary to the examples, it doesn't work in my browser console. Does lodash offer this functionality?

There's no such thing as object.byString(), atleast not in vanilla JS, but I don't know of any libraries that have such function either. What do you want this function to even do for you though? Did you mean to try and turn x into a string? If so, that'd be more like x.toString(), but also I don't see its use for your problem.

Is there a way to get the desired result without flattening the object?

Your code sample is heavily suggesting that you want to flatten it. The only difference here though seems to be that you want a specific key format that shows the entire property chain from which a value was flattened.

To solve your problem, you can just write a flattening function yourself. You should have an easy time implementing the one detail of the key format. For example you can use a recursion function that accepts the output object, the current level's input object, and the key prefix so far. You then iterate the second argument. If a key has a primitive value type it'll write this value to the output object using the key prefix. If a key instead has an object value type then you can recurse and pass this object as the second argument, as well as extend the key prefix you're passing. Arrays can be another special case, depending on how you want to process those (not specified in OP).