So, some Feren OS Users might be experiencing the complete loss of 'Themes' from System Settings or that the 'Themes' window lacks Feren OS Theming Support but is instead the one found in Vanilla Cinnamon... here's how to fix it:
1. Open up a Terminal
To do this, open up your applications menu and search for 'Terminal'. Once it's found, open it up, and proceed.
2. Run the following commands with no quotes:
sudo apt-get update
sudo apt-get install --reinstall feren-themer feren-themer-cinnamon feren-*-layout-cinnamon -y
You'll need to authenticate with Sudo Privileges to perform the package operations, hence the need to be an administrator. If you don't know what a Sudo Password is, it's the exact same password as the password used to log in as the user it wants the '[sudo] password' for.
3. Try opening Themes now
Assuming the command finished successfully, you should now be able to use Themes for Feren OS again instead of Vanilla Cinnamon's Themes section or no Themes section at all.