Hi there, @Ellaifi. From what you've described, it would appear that you may have inadvertently activated grayscale (which can be helpful in some situations) on your S21.To ensure that you get your phone to display in glorious colour again, I recommend consulting and following the steps in the guide below (created by our colleagues from Samsung Singapore):https://www.samsung.com/sg/support/mobile-devices/how-to-troubleshoot-when-the-samsung-phone-display...
Just in case you've only toggled this on via the Camera app, the guide below (from Samsung Australia) should facilitate you in restoring colour to your photos:
Effectively, you'd just need to remove the filter.I trust that these steps will help. Please let me know.