Getting subfield of "post" field type

Hello,

I have 2 CPT "concert" and "artiste".

I am using Oxygen Builder and am trying to link a concert with several artists, in order to display their biography (content), title, photo (thumbnail image) and other custom fields.

I decided to use the "post" field type, cloneable to get the artists as concert fields.
(I was thinking of using MB relationships but didn't manage to make it work)

I try to display their biography and instrument in a code block :

<?php $post_ids = rwmb_meta( 'artiste_s_associe' ); 
  
  foreach ( $post_ids as $post_id ) : 
    $nom_artiste = get_the_title( $post_id );
    $instrument = rwmb_meta( 'instrument' );
    $biographie = get_the_content( $post_id );
    $photo = get_the_post_thumbnail_url( $post_id);
?>
    <h3><?php echo $nom_artiste; ?> - <?php echo $instrument; ?></h3>
        <div> <?php echo $biographie; ?>
<?php endforeach
?>

The value $nom_artiste displays the correct names, but I cannot reach out to have the content, it displays the content of the global post ID. Which function should I use ? Also, the custom fields are not showing, I suppose it's the same problem.

Could you tell me where I am wrong ?

Thank you,