Finally got around to cleaning up all the (broken) auto-posts from IFTTT that I’d long forgotten about, and it led me to generate a bookmarklet that might help you delete posts more easily from your WordPress blog as well:
// Delete top post from "Posts" admin page (https://wordpress.com/posts/<your-site-name>)
javascript: (() => {
document.querySelector('button[title="Toggle menu"]').click();
document.querySelectorAll('button[role="menuitem"]')[2].click();
})();