When the screen is locked, it flickers for about 1 second before the lock screen appears.

The one-second flash during Win+L is likely part of the display-driver transition to the lock screen, not the animation setting. Microsoft’s guidance separates driver problems from incompatible apps. Press Ctrl+Shift+Esc, leave Task Manager visible, then lock and unlock the PC and note whether it flashes too. Press Win+Ctrl+Shift+B to reset the graphics driver. If the issue began after a driver or Windows update, roll back the display driver in Device Manager; otherwise install the PC maker’s recommended driver, or uninstall the display adapter and restart so Windows reinstalls it. Test after disconnecting docks and monitors and temporarily disabling HDR, variable refresh rate, overlays, and recording utilities. If Task Manager does not flicker, clean-boot Windows and re-enable startup apps in groups to find the incompatible component. If the flash persists without crashes or artifacts, record it and submit Feedback Hub data with the Windows build, GPU, driver version, and monitor configuration