sanitize-form-fields.php

<?php

add_filter( 'jet-form-builder/form-handler/form-data', function( $request ) {
  if ( isset( $request['field_name_to_sanitize'] ) ) {
    $request['field_name_to_sanitize'] = wp_strip_all_tags( $request['field_name_to_sanitize'] );
  }
  return $request;
} );