.form-control.form-control-readonly[readonly] {
  background-color: var(--bs-gray-100);
  border-color: var(--bs-gray-400);
  color: var(--bs-gray-600);
  opacity: 1;              /* importante: evita look "disabled" */
  cursor: default;         /* oppure not-allowed se vuoi più esplicito */
}

.form-control.form-control-readonly[readonly]:focus {
  box-shadow: none;
  border-color: var(--bs-gray-400);
}