Codex windows app 26.527.31326 fullscreen focused window becomes transparent #25235

What version of the Codex App are you using (From “About Codex” dialog)?

26.527.31326

What subscription do you have?

ChatGPT Free

What platform is your computer?

Windows 10.0.19044 x64

What issue are you seeing?

After the latest Codex Windows app update, Codex has a fullscreen rendering issue.

When the Codex window is fullscreen/maximized and focused, part of the app becomes visually transparent and the Windows desktop icons show through the Codex window.

If I click the Windows taskbar so Codex loses focus, the window renders normally again. When I click back into Codex, the issue returns.

This did not happen on the same computer with previous Codex versions.

Transparency effects are disabled in Windows, but the issue still happens.

What steps can reproduce the bug?

1. Open Codex Windows app.
2. Maximize/fullscreen the Codex window.
3. Click inside Codex so the app is focused.
4. Observe that part of the Codex window becomes transparent and the desktop shows through.
5. Click the Windows taskbar so Codex loses focus.
6. Observe that Codex renders normally while unfocused.
7. Click Codex again.
8. The transparency/rendering issue returns.

What is the expected behavior?

Codex should render normally while fullscreen/maximized and focused.

Additional information

GPU: AMD Radeon HD 8950
GPU driver: latest available
Display: 1920x1080, 100% scaling
OS transparency effects: disabled

This looks like a Windows/Electron/Chromium GPU compositing regression in the recent Codex Windows app update, possibly related to fullscreen focused rendering. It does not look like a missing Visual C++/.NET runtime issue because the app launches and works normally except for this fullscreen focused rendering problem.