Decompiling

Decompiling the game extracts files from the game .pck file and converts them from formats native to the engine to user-friendly formats.
Optionally, the game can be converted into a Godot project, allowing debugging and hotloading.

Extracting and decompiling

The game files can be extracted using Godot RE Tools and GodotPckTool.

Godot RE Tools

After downloading the program, select "RE Tools">"Recover project..." from the menu and pick the .pck of the game.
If you wish to extract the game files without decompilation, chose the "Extract only" option, otherwise chose "Full Recovery". This will decompile the game and produce a working Godot project. This process may take a long time.
If you wish to decompile the files after extracting them, you can use the "GDScript" and "Resources" options in the menu.

After decompiling the project, you can open it using Godot 4.3 from here https://godotengine.org/download/archive/#4.3 .
After you open the project in the editor, the editor may re-import the textures as it detects they're being used in 3D and generates mip-maps for them. This process may take a long time but the editor will be partially usable.

GodotPckTool

GodotPckTool is a command-line only program for manipulating .pck files.
To extract a .pck using this tool, use the following options:

godotpcktool /path/to/game.pck --action extract --output /path/to/output

The output files can be decompiled individually using Godot RE Tools.