Custom (Advanced) installation option missing in Pop!_OS 24.04 COSMIC installer

[tscaramel]

Description

The Custom (Advanced) installation option is not appearing in the Pop!_OS 24.04 COSMIC installer, preventing the two-pass btrfs installation method documented at https://mutschler.dev/linux/pop-os-btrfs-24-04/

Hardware

• System76 Serval WS
• Pop!_OS 24.04 LTS stable release

Steps to Reproduce

1. Boot from Pop!_OS 24.04 ISO
2. Launch "Install Pop!_OS" from Applications
3. Progress through language/region selection
4. Select keyboard layout
5. Expected: Screen offering "Clean Install", "Custom (Advanced)", and "Try Demo Mode" options should appear
6. Actual: Installer skips directly to user account creation screen - no installation type selection screen appears at all

Impact

• Cannot install with btrfs filesystem using the recommended two-pass method
• Cannot access any custom partitioning options
• No way to select installation type - installer appears to assume "Clean Install" by default
• This affects System76 hardware owners who want btrfs with proper subvolumes for Timeshift
• Completely blocks advanced installation scenarios (dual boot, custom partitioning, btrfs setup)

Expected Behavior

After keyboard layout selection, the installer should display a screen with installation type options:

• Clean Install
• Custom (Advanced) - to access GParted for manual partitioning
• Try Demo Mode

This screen exists in Pop!_OS 22.04 and is documented in official guides.

Additional Context

The official System76 support docs still reference this option: https://support.system76.com/articles/install-pop/
Multiple guides assume this functionality exists for btrfs setup.

This appears to be a more severe issue than just a hidden button - the entire installation type selection screen is being skipped in the COSMIC installer.

Request

Please restore the installation type selection screen in the COSMIC installer to allow access to Custom (Advanced) partitioning options.