look this sample: https://support.google.com/adsense/answer/10762946?hl=en&ref_topic=9183242&sjid=8011425263000445431-NA#:~:text=Hiding%20unfilled%20ad-,units,-using%20CSS

CSS:

ins.adsbygoogle[data-ad-status="unfilled"] {
display: none !important;

}