app/node_modules/ng-zorro-antd/select/style/patch.less

.ant-select-dropdown {
  position: relative;
  top: 100%;
  left: 0;
  display: block;
  width: 100%;
  margin-top: 4px;
  margin-bottom: 4px;

  .cdk-virtual-scroll-content-wrapper {
    right: 0;
  }

  .full-width {
    contain: initial;

    .cdk-virtual-scroll-content-wrapper {
      position: static;
    }

    .cdk-virtual-scroll-spacer{
      position: absolute;
      top: 0;
      width: 1px;
    }
  }
}