MyProject/app/views/main_view.php

<div class="row mt-3">
    <div class="col-6">
        <h1>Блог</h1>
    </div>
    <div class="col-6 text-end">
        <?=$_SESSION['user']['login']; ?>
        <a href="/user/logout">Выход</a>
    </div>
</div>

<form action="/main/createpost" method="post">
    <div class="row my-3">

        <div class="col-12">
            <a  data-bs-toggle="collapse" href="#createform" role="button" aria-expanded="false" aria-controls="collapseExample">
                Создать пост
            </a>
            <div class="collapse" id="createform">
                <input required minlength="3" class="form-control mt-3" type="text" name="caption" placeholder="Заголовок">
                <textarea required minlength="10" class="form-control mt-3" name="post" placeholder="текст поста"></textarea>
                <div class="text-end mt-3">
                    <button class="btn btn-primary" type="submit">Создать</button>
                </div>
            </div>
            <hr>
        </div>
    </div>
</form>


<?php
var_dump($posts);
?>