With the last version of WP (5.4) and as toolbar extra isn't tested yet on this version, it produces some "fatal" error when i want to install it.
I think it's due to MailPoet plug in.
Une erreur de type E_ERROR a été causée dans la ligne 106 du fichier /var/www/vhosts/titanscity.com/httpdocs/wp-content/plugins/toolbar-extras/includes/plugins-forms/items-mailpoet.php.
Message d’erreur : Uncaught Error: Undefined class constant 'TYPE_LISTING_EDITOR' in /var/www/vhosts/titanscity.com/httpdocs/wp-content/plugins/toolbar-extras/includes/plugins-forms/items-mailpoet.php:106 Stack trace: #0 /var/www/vhosts/titanscity.com/httpdocs/wp-includes/class-wp-hook.php(287): ddw_tbex_site_items_mailpoet(Object(WP_Admin_Bar)) #1 /var/www/vhosts/titanscity.com/httpdocs/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array) #2 /var/www/vhosts/titanscity.com/httpdocs/wp-includes/plugin.php(544): WP_Hook->do_action(Array) #3 /var/www/vhosts/titanscity.com/httpdocs/wp-includes/admin-bar.php(97): do_action_ref_array('admin_bar_menu', Array) #4 /var/www/vhosts/titanscity.com/httpdocs/wp-includes/class-wp-hook.php(287): wp_admin_bar_render('') #5 /var/www/vhosts/titanscity.com/httpdocs/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters('', Array) #6 /var/www/vhosts/titanscity.com/httpdocs/wp-includes/plugin.php(478): WP_Hook->do_action(Array) #7 /var/www/vhosts/titanscity.com/httpdocs/wp-adm