Version 4 removed the file sharing feature as written in the changelogs:
Cautions
- Your settings can NOT be kept when upgrading to this version from 3.x. Please backup your settings first.
- This version firmware does NOT include the following features:
- File Sharing
- Captive Portal
- RS485
- GPS
- Mesh
- This admin panel does NOT include the following languages:
- French
- Korean
- Russian
- Limited by CPU performance and storage space, this version firmware also does NOT include Network Storage fature. (Allow users to install via plug-in after exroot)
You have to exroot before you can install those plugins again: