ElMessageBox.confirm(
          `导入结果：<br/>成功导入${res.successCount}条数据，导入失败${res.errorList.length}条数据。<br/>${str}`,
          "提示",
          {
            confirmButtonText: "确定",
            cancelButtonText: "取消",
            type: "warning",
            dangerouslyUseHTMLString: true,
          }
        )
          .then(() => {
           
          })
          .catch(() => {
           
          });

直接加入dangerouslyUseHTMLString 属性就可以识别标签了