This official absence is what has led the homebrew and modding community to create their own solution. By leveraging the PS4's native PS2 emulator, which Sony itself uses for its official Classics, the community has found a way to run any PS2 game on the console through a custom "fake PKG" (FPKG) file.
Early attempts at creating a Gran Turismo 4 PS4 PKG suffered from severe visual bugs. Players often encounter broken textures, missing shadows, or flickering menus. Specific emulation configurations (known as LUA fixes) are required to fix these issues. Framerate Drops Gran Turismo 4 Ps4 Pkg