Cannot get pdf thumbnail V4 to V5 upgrade

[FoxRocks76]

I'm running Laravel v5.4 (currently upgrading it) and Laravel Valet. I've been following the instructions, and noted the requirement to have imagick for pdf thumbnails. I used Homebrew to install it, I've confirmed that imagemagick is installed ($ convert -version), and that imagick php extension is loaded (php -r 'echo "imagick is ".(extension_loaded("imagick")?"":"not ")."installed\n";'). I have 'image_driver' => 'imagick',set in the config, which I've renamed to "medialibrary.php" as per the instructions. My file uploads as expected, but it's the thumbnail that isn't being generated. This was working in v4, so I've obviously messed up on the upgrade somewhere. Anyways, here is the code in my model:

     * Create a thumbnail for every media upload on this model
     */
    public function registerMediaConversions()
    {
        // Perform a resize and sharpen on every collection
        $this->addMediaConversion('thumb')
              ->width(368)
              ->height(232)
              ->sharpen(10)
              ->optimize();
    }