I'm pretty sure that's because the entire <main> of the site has an 8px Gaussian blur on it:

  .site-main[data-astro-cid-bpoqdqeq] { 
    backdrop-filter:blur(8px); 
  }

Why, exactly? The page looks visually identical when I disable that rule, but the performance skyrockets. I realize that it's probably vibecoded, but come on.