@Michael Oud: Please try heading to Settings > Device care > Storage, and check to make sure that you have sufficient storage space available on your phone to house the image files. If you do, please head to Settings > Apps > Camera > Force stop > Storage > Clear cache, followed by Settings > Apps > Gallery > Force stop > Storage > Clear cache, then restart your Galaxy S21 FE. This will resolve any temporary software/performance issues with the device. Let me know how you get on.
@Michael Oud: I'm sorry to hear that you have encountered further issues with Camera app. If you head to the Samsung Members app > Press and hold on the app icon > Diagnostics > Phone diagnostics > Camera, and follow the on-screen prompts, does this return an 'Action required' notification in the summary at the end of the test?
To further troubleshoot the issue, please restart your phone in Safe mode, as this will disable all third party apps and help to verify if the problem is stemming from an external factor. To enter Safe mode, press and hold the Power button until the 'Power off' prompt appears on the screen then release > Touch and hold Power off until the 'Safe mode' prompt appears then release > To confirm, tap Safe mode.
With Safe mode active, monitor the performance of the device for a few hours, based on the frequency that you encounter the issue. If you find that the camera works as normal, then please restart your S21 FE as you would normally and uninstall any apps that you have added to the device since you first encountered the issue. It won't be possible to determine exactly which app is at fault, therefore we recommend approaching this via a process of elimination.
