To address the issue of apps opening in a non-maximized window in a LineageOS 23.0 virtual machine running under Virtual Machine Manager (virt-manager), the solution typically involves adjusting the window management settings of the virtual machine itself, rather than the guest OS (LineageOS).

Here are the most effective steps:

1. Adjust virt-manager Display Settings

• Open Virtual Machine Manager.
• Select your LineageOS VM and click Open to start it.
• In the VM window, go to View > Fullscreen or press Host+F (usually Right Ctrl+F or Left Ctrl+F depending on your host OS) to toggle fullscreen mode.
• If the VM window is not maximizing properly, try resizing the window manually and then use the fullscreen shortcut again.

2. Edit VM XML Configuration

• In Virtual Machine Manager, go to Edit > Preferences > General and enable XML editing.
• Shut down the VM.
• Right-click the VM and select Edit XML.
• Look for the <graphics> section and ensure it includes attributes like autoresize=yes or listen=0.0.0.0 (if using SPICE/QXL).
• Save and restart the VM.

3. Guest OS Settings (LineageOS)

• Inside LineageOS, go to Settings > Display and check if there is an option for Window size or Screen resolution. Set it to match your host display.
• Some Android/LineageOS builds for VMs may require you to install a window manager app (like "Taskbar" or "Android Tools") from F-Droid to force apps to open in fullscreen.

4. Use a Different Graphics Driver

• In the VM XML, try changing the graphics type from spice to vnc or sdl and see if the behavior improves.

Note: If the issue persists, it may be due to the specific build of LineageOS 23.0 for QEMU/virtualization. The LineageOS Wiki and community forums (like Reddit) suggest that QEMU-based LineageOS 23.0 is still evolving, and some window management quirks are knownwiki.lineageos.org+2.

Would you like help troubleshooting a specific step further?