could you try on a computer, if it's working then it'steam's deck related, you can try to change de rendering, d3d11, vulkan ... as i own no deck for testing i can solve that on my side
On my PC, everything is fine, even when using Steam Deck OLED preset.
Further testing on Deck:
Game Mode, Steam Deck OLED preset:
OpenGL - Backgrounds load, but models invisible.
D3D9 - No picture (but game is running, can hear sound response to button press).
D3D11 - No problem with poly lines, but colours wrong.
D3D12 - No problem with poly lines, but colours wrong.
Vulkan - Original problem with poly lines, but colours correct.
Dekstop mode, Steam Deck OLED preset:
OpenGL - No response to controls at New Game/Continue screen.
D3D9 - Satsuki splash screen & audio appears, then no picture or audio response to button press.
D3D11 - ** No graphical problems **; intermittent, very minor input lag.
D3D12 - ** Perfect! **
Vulkan - Original problem with poly lines returns.
So, my problem is solved with D3D12 in Desktop mode.
Maybe a Vulkan issue?
Doesn't matter to me, but FYI the game fails to launch when Steam Achievements option is selected, even in Desktop mode with Steam open.
If I can ever help you by testing on my Steam Deck OLED, please let me know and I will try to assist
Thank you for your help!