Some Samsung devices have issues with a flickering screen when a popup is shown (keyboard input or list selection).
This is caused by a bad driver implementation.
Make sure you've installed the latest OS updates. Samsung already fixes this issue for most devices.
- Activate developer settings in your device
- Settings -> About phone -> Tap 6x Times on "Build number"
- Disable hardware overlays
- Settings -> Developer options -> Check "Disable HW-Overlays"
Note: These settings might be reversed when restarting the device.