It looks like the namespace for the debugger has changed to Sober\Controller\Debugger as per the source found here: https://github.com/soberwp/controller/blob/2.0.0/src/Debugger.php
Errors about “Class ‘SomeClass’ not found” or about “ReflectionError” frequently mean that the namespace or class name is wrong either where a class is being instantiated, or in the original definition of that class. If you’re struggling with namespaces, this post I wrote attempting to explain how they work may be helpful: Controller namespace issue, different behavior on localhost and development server