AmCharts 4 环形图可以通过添加自定义的 URL 超链接来实现。以下是一个包含代码示例的解决方法：

// 导入 AmCharts 相关模块
import * as am4core from "@amcharts/amcharts4/core";
import * as am4charts from "@amcharts/amcharts4/charts";
import * as am4interfaces from "@amcharts/amcharts4/.";
import am4themes_animated from "@amcharts/amcharts4/themes/animated";

// 引入主题
am4core.useTheme(am4themes_animated);

// 创建图表实例
var chart = am4core.create("chartdiv", am4charts.PieChart);

// 设置数据
chart.data = [
  { category: "分类1", value: 100, url: "http://example.com" },
  { category: "分类2", value: 200, url: "http://example.com" },
  { category: "分类3", value: 150, url: "http://example.com" }
];

// 创建环形图系列
var series = chart.series.push(new am4charts.PieSeries());
series.dataFields.value = "value";
series.dataFields.category = "category";
series.slices.template.propertyFields.url = "url";

// 创建标签模板
var label = series.slices.template.labels.template;
label.wrap = true;
label.maxWidth = 120;
label.text = "{category}";

// 创建切片点击事件
series.slices.template.events.on("hit", function(event) {
  var url = event.target.dataItem.dataContext.url;
  window.open(url, "_blank");
}, this);

// 将图表添加到页面中
chart.exporting.menu = new am4core.ExportMenu();
chart.exporting.menu.align = "right";
chart.exporting.menu.verticalAlign = "top";
chart.exporting.menu.items = [
  {
    "label": "...",
    "menu": [
      { "type": "png", "label": "PNG" },
      { "type": "jpg", "label": "JPG" },
      { "type": "svg", "label": "SVG" },
      { "type": "pdf", "label": "PDF" },
      { "type": "json", "label": "JSON" },
      { "type": "csv", "label": "CSV" },
      { "type": "xlsx", "label": "XLSX" },
      { "type": "html", "label": "HTML" }
    ]
  }
];

上述代码中，我们首先导入了 AmCharts 相关模块和主题。然后，创建了一个环形图实例，并设置了数据。接着，创建了一个环形图系列，并通过设置 slices.template.propertyFields.url 属性来指定每个切片的 URL。然后，创建了一个标签模板，并设置了标签的显示样式。最后，创建了一个切片点击事件，当用户点击切片时，将在新标签页中打开对应的 URL。

最后，将图表添加到页面中，并设置了导出菜单选项。