At a guess, it's because you've defined Awake as "Private"

Monobehaviour comes with Awake as part of its class.
What you're doing by referencing it in PlayerMovement is saying "use my version, not the default one".
It won't be Private in Monobehaviour though, it's meant to be inherited and overriden by another class.
By defining it as Private, you're breaking the linkage between PlayerMovement and the Monobehaviour that it derives from.
You're saying you want a function called Awake that is unique to PlayerMovement.
Which you can't do because you're inheriting from Monobehaviour which already has one, and that's what the error is saying. It doesn't understand which one to use, because you've broken the semantic link between them.

So your fix should be to remove the word "Private" from the Awake line.

void Awake()