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I scraped the WordPress source code to find this solution that is in pure PHP, without using javascript, and it has been available since WordPress 4.4

You can use the action "manage_posts_extra_tablenav" to insert whatever you want after the "filter" button, both before and after the table.

https://developer.wordpress.org/reference/hooks/manage_posts_extra_tablenav/

This is an example:

add_action('manage_posts_extra_tablenav', function($which) {
    if (get_current_screen()->post_type !== 'ticket'){
        return;
    }
    echo '<div class="actions alignleft"><button>Custom button</button></div>';
});