<div class="element-parent">
  <div class="element-opacity">
    <div class="element-texte">Mon texte</div>
    <img src="https://picsum.photos/id/347/300/450" class="element-image">
  </div>
  <div class="element-filter">
    <div class="element-texte">Mon texte</div>
    <img src="https://picsum.photos/id/347/300/450" class="element-image">
  </div>
</div>

.element-parent {
  --valeur: 0.7;
}

.element-parent {
  position: relative;
  display: grid;
  grid-template-columns: repeat(2, 300px);
  gap: 1px;
  max-height: 450px;
  overflow: hidden;
  background-color: green;
  width: 600px;
}

.element-texte {
  position: absolute;
  top: 64px;
  left: 112px;
  font: 4.5em Georgia, serif;
  color: #fff;
  z-index: 5;
}

.element-filter .element-image {
  position: relative;
  z-index: 1;
  filter: brightness(var(--valeur));
}

.element-opacity {
  background-color: #000;
}

.element-opacity .element-image {
  position: relative;
  z-index: 1;
  opacity: var(--valeur);
}