How do I disable APC caching just changing any Drupal setting? Is it possible to disable APC caching completely in Drupal 8 without modifying the php.ini settings (i.e. only by modifying the Drupal settings)?
There are multiple settings necessary to do so:

in active settings.php:

/**
 * Class Loader.
 *
 * If the APC extension is detected, the Symfony APC class loader is used for
 * performance reasons. Detection can be prevented by setting
 * class_loader_auto_detect to false, as in the example below.
 */
$settings['class_loader_auto_detect'] = FALSE;

// Default cache backend.
$settings['cache']['default'] = 'cache.backend.database'; // or any other alternative cache backend


After looking at Berdirs comment and diving further into code and looking at more usages of apcu within Drupal it appears to be pretty much impossible to catch every usage / and even if you manage to find all of them - disabling at some points is not possible (e.g. no configuration options present).