How to backup and restore iPad apps locally on a Windows machine? (without re-downloading from internet) (also resume app downloads)
This article from OSXDaily Get iTunes 12.6.3 with App Store for Mac and Windows suggests to download the special 12.6.3 version, which restores the previous lost functionality.
Do not know if works without internet in your case.

Also, the newest version 12.7, when connecting the first time a device, asks if you like to restore the old feature - this was the behaviour in my case.

Direct link to this version of iTunes download page: https://support.apple.com/kb/HT208079