Ejemplo columnas con multiples media queries

columnas.css

.grid {
  display: grid;
  gap: 20px;
  width: 90%;
  margin: 0 auto;
}

@media(min-width: 1100px) {
  .grid {
    grid-template-columns: 1fr 1fr;
  }
  .grid :first-child {
    grid-column-end: span 2;
  }
}

@media(min-width: 780px) and (max-width: 800px) {
  .grid {
    grid-template-columns: 1fr 1fr;
  }
  .grid :first-child {
    grid-column-end: span 2;
  }
}