具体的操作步骤如下：

步骤一：打开Beyond Compare软件，点击上方的“工具”菜单，选择“选项”命令

步骤二：左侧选择“启动”栏目，右侧勾选“在资源管理器环境菜单中包含Beyond Compare”，并在“比较”命令右边位置点击下拉按钮，选择主菜单

点击确定就OK了。

测试：（注意：如果不好使请看最后）

选择一个或多个文件可看到效果

如果还是不好使，可以参照官网解决办法
https://www.scootersoftware.com/support.php?zz=kb_shellex

SHELL EXTENSION NOT DISPLAYED

If the shell extension is checked in the options dialog but it isn't displayed in Windows Explorer's right-click menu, applying registry patches will often fix the problem.

Beyond Compare 4 registry patch:  BC4ShellExFix.zip
Beyond Compare 3 registry patch:  BC3ShellExFix.zip

To apply the registry patches:

1. Uninstall Beyond Compare.
2. Download the registry patch zip file that matches your Beyond Compare version and unzip it.
3. Double click on Remove.reg to remove Beyond Compare's shell extension registry entries.
4. Reboot.
5. Install Beyond Compare 3.3.13 or the current version of Beyond Compare 4.
6. If Beyond Compare is installed to a location other than the default folder (C:\Program Files\Beyond Compare 4), edit the installation path in Add_64-bit.reg or Add_32-bit.reg.
7. Double click on Add_64-bit.reg or Add_32-bit.reg to add Beyond Compare's shell extension registry entries.  Use patch that matches the architecture (32-bit or 64-bit) of your operating system.
8. Reboot.

翻译过来就是：（但是并不需要这么麻烦，直接执行步骤2，3，6应该就可以了）

1. 卸载BCompare
2. 下载对应BCxShellExFix.zip，并解压
3. 双击Remove.reg来移除BCompare的右键扩展功能菜单；
4. 重启电脑
5. 重新安装BCompare
6. 根据电脑的位数选择脚本：Add_32-bit.reg，Add_64-bit.reg。如果修改了BCompare的默认安装路径，则需要修改对应脚本中涉及到的BCompare路径
7. 再执行一次步骤6
8. 重启电脑