UninstallView is a freeware tool for Windows which allows you to view the installed programs on your local system, remote system, and on external drive.
In order to list the installed Windows applications on external drive, you have to plug the hard drive into your system and then follow the instructions below:

1. Run UninstallView, and then press F9 to open the 'Advanced Options' window.
2. In the 'Advanced Options' window, choose 'External drive' from the 'Load From' combo-box.
3. Fill the root folder field with the drive letter of the external drive (e.g: F:\).
4. UninstallView will automatically fill for you the other 2 fields - Config Folder ( f:\Windows\System32\Config ), and Users folder ( f:\Users ). If from some reasons these folders are not correct, you have to type the correct folders.
5. Press the 'Ok' button to start reading the installed application data from the external drive.
6. If you want to list the installed Windows 10 apps, you should turn on the 'Load Windows Apps' option (Under the Options menu).

Export to a file from command-line.

UninstallView also allows you to export the install programs on external drive directly to a file, without displaying any user interface.
For example, the following command exports the install programs on drive G:\ to a comma-delimited (csv) file:
UninstallView.exe /LoadFrom 5 /RootFolder "G:\" /ConfigFolder "G:\Windows\System32\Config" /UsersFolder "G:\Users" /scomma "c:\temp\installed_programs.csv"