Website crashed with smugh

Hello there @marthe1992,

hope you’re doing good and I’m really sorry for this experience with Smush!

In case your site becomes completely unresponsive, then you should connect to your server via (S)FTP and delete the plugin by deleting the
wp-content/plugins/wp-smushit/ folder.

In order to troubleshoot this though, could you please access your server via (S)FTP, edit wp-config.php file, find a line like
define('WP_DEBUG', false); and replace it with the following (if the above line doesn’t exist, simply insert next snippet just above the /* That’s all, stop editing! Happy blogging. */ comment)

// Enable WP_DEBUG mode
define('WP_DEBUG', true);
// Enable Debug logging to the /wp-content/debug.log file
define('WP_DEBUG_LOG', true);
@ini_set( 'log_errors', 1 );
// Disable display of errors and warnings
define('WP_DEBUG_DISPLAY', false);
@ini_set('display_errors', 0);

Then go ahead and try to replicate the error by re-installing Smush.
By doing so, a /wp-content/debug.log file should be created. Simply download it, remove any sensitive data, use a service like Dropbox and post the shareable link in your next reply.
Ref: https://premium.wpmudev.org/blog/debugging-wordpress-how-to-use-wp_debug/

Warm regards,
Dimitris