Windows desktop app's sidebar icons vanish, conversations empty, and login button does nothing after logout (browser works fine)

Same: Windows 11 Pro 25H2 ChatGPT Desktop 1.2026.133.0 (Microsoft Store) Browser and Android work normally. Repair, Reset, uninstall, reinstall, and reboot did not help. Upper-right Log In button does nothing. Lower-left Log In closes the sidebar but does not open authentication. Sign Up button also does nothing. Entering a prompt while logged out results in a blank screen. Codex desktop app launches normally.