if condition from post_meta not working in save_post

Question

I'm new to Wordpress, and I am trying to make a condition to run something in save_post if a checkbox is enabled.

Right now my code is like this:

add_action( 'save_post', 'ac_verifica_links' );

function ac_verifica_links($post_id) {
    remove_action( 'save_post', 'ac_verifica_links' );
    update_post_meta( $post_id, 'ac_desabilitar_links', $_POST['ac_desabilitar_links']);
    if ($_POST['ac_desabilitar_links'] != "sim") {
        // do something
    }
    add_action( 'save_post', 'ac_verifica_links' );
}

add_action( 'add_meta_boxes', 'ac_adiciona_checkbox' );
function ac_adiciona_checkbox() {
    add_meta_box('ac_desabilitar_links_id','Desabilitar Links?', 'ac_desabilitar_links_callback', 'post', 'normal', 'high');
}
function ac_desabilitar_links_callback( $post ) {
    global $post;
    $desabilitarLinks = get_post_meta( $post->ID, 'ac_desabilitar_links', true );
    ?>

    <input type="checkbox" name="ac_desabilitar_links" value="sim" <?php echo (($desabilitarLinks == 'sim') ? 'checked="checked"': '');?>/> Sim
    <?php
}

The meta post checkbox work as normal, saving correctly and all. But, for some reason, the conditional if ($_POST['ac_desabilitar_links'] != "sim") always returns true.

What exactly am I doing wrong here? I'm having a hard time debugging this, as gutenberg doesn't print anything from save_post.

Thanks for your time!