Where are the apps in ITUNES

Apple removed all App management from iTunes starting with iTunes 12.7. All app management is now done directly on the relevant devices.

Changes in the new iTunes - Apple Support

All download Apps remain in the Mobile Applications folder inside the iTunes Media folder however, and you can still drag them onto the device on the iTunes side bar to sync.

If you need to have the App management sections in iTunes, you can download iTunes 12.6.3 for bussinesses which still has the option:

Deploy apps in a business environment with iTunes - Apple Support

Manually manage content on your iPhone, iPad, or iPod touch using iTunes - https://support.apple.com/HT201593 - "Manually add items from your computer: If you have media on your computer that you can't redownload from the App Store or iTunes Store directly on your iOS device, such as custom ringtones or iOS apps, you can drag and drop the media from your computer to your iOS device using iTunes."

Deploy apps in a business environment with iTunes - Apple Support - https://support.apple.com/HT208079 - Downgrade to iTunes 12.6.3

Gone.

Changes in the new iTunes [12.7] - https://support.apple.com/HT208075

Managing apps with iTunes 12.7 or later - https://discussions.apple.com/docs/DOC-12234