But here is some sloppy code you could create a basic browser extension and shove in content.js:

  function hideVerticalVideos() {
    const videos = document.querySelectorAll('video');
    videos.forEach(video => {
      if (video.videoHeight > video.videoWidth) {
        video.style.display = 'none';
      }
    });
  }

  // Run hideVerticalVideos() when the page loads
  window.addEventListener('load', hideVerticalVideos);

  // Run when the DOM updates
  const observer = new MutationObserver(hideVerticalVideos);
  observer.observe(document.body, { childList: true, subtree: true });

Safari in particular has never worked, but I've had bad luck with Chrome and Firefox as well.

On a related note, is there a browser that can completely block auto-playing video with a setting that actually works?

I find it depressing that web developers seem willing to do anything to ignore user preferences, especially when intrusive advertising is involved.