There are several ways you could make your code less monolithic. The easiest is to just take everything under your outermost matches and put it in a separate function. That way, the main function (_physics_process) is easier to read.
You could also take repetitive code and make functions out of it. The only difference between your left and right code is the objects affected. You could make a function that uses variables for the AtkCollR and AtkCollL and assign them to each variable based on a parameter to the function. But, I wouldn't worry too much about that, because you've only used it twice anyway.
