Fix for loading Ninja forms preview in Sage theme version 10

app.ninja-forms.php

<?php

namespace App;

/**
 * Set preview page for ninja forms
 */
add_filter('template_include', function ($template) {
    if (substr($template, -9) === 'index.php') {
        $ninja_forms_id = isset($_GET['nf_preview_form']) ? $_GET['nf_preview_form'] : null;

        if ($ninja_forms_id) {
            $blade_template = locate_template('resources/views/ninja-forms-preview.blade.php');
            return ($blade_template) ? $blade_template : $template;
        }
    }

    return $template;
});

resources.views.ninja-forms-preview.blade.php

@extends('layouts.app')

@section('content')
  @while(have_posts())
    @php
    the_post();

    $ninja_forms_id = isset($_GET['nf_preview_form']) ? $_GET['nf_preview_form'] : null;
    @endphp

    <article class="container mx-auto mb-8">
      <div class="px-5 mt-8 md:my-16 xl:mt-20">
        <div class="max-w-screen-md mx-auto">
          @if ($ninja_forms_id)
            {!! do_shortcode("[ninja_form id=$ninja_forms_id]") !!}
          @endif
        </div>
      </div>
    </article>
  @endwhile
@endsection