To hide the title bar in KWin, you can use the following steps:
1. **System Settings**: Open System Settings.
2. **Window Management**: Navigate to "Window Management".
3. **Window Rules**: Go to "Window Rules".
4. **Add New Rule**: Click on "New" to add a new rule.
5. **Window Matching**: Set the criteria to match the window you want to hide the title bar for.
6. **Appearance & Fixes**: Go to the "Appearance & Fixes" tab.
7. **No Titlebar and Frame**: Check the option "No titlebar and frame".
Apply and save the settings. This should hide the title bar for the specified window.