Update Asset Indexes gives "getFileList() is not implemented"
This exception in thrown in the class craft\volumes\MissingVolume that states one of your Volumes has an invalid class 

/**
 * @inheritdoc
 */
public function getFileList(string $directory, bool $recursive): array
{
    throw new NotSupportedException('getFileList() is not implemented.');
}


Maybe you uninstalled a plugin that adds a certain Volume class like S3 or something?