This snippet stops the form from being submitted if the name matches any of the blocked names stored in an array.

wpf-block-names.php

<?php

add_action( 'wpforms_process_validate_name', function( $field_id, $field_submit, $form_data ) {
 
  // Bail early if form ID is not 2090 and field ID is not 1
  if ( absint( $form_data['id'] ) !== 2090 && $field_id !== 1 ) {
    return;
  }

  $submitted_name = $field_submit['first'] .' ' .$field_submit['last'];

  // Create your list of names to be blocked separated by commas
  $blocked_names = array( 
    'Eric Eric', 
    'Lucia Lucia',
    'Johan Johan'
  );

  foreach( $blocked_names as $name ) {
    if( strcmp( $submitted_name, $name ) == 0 ) {
        wpforms()->process->errors[ $form_data['id'] ]['header'] = esc_html__( 'Can\'t submit form. Please try again later.', 'wpforms' );
        return;
    }
  }
  
}, 10, 3 );