Hi
@Vonntelll Welcome to the Samsung Community
😁Whilst there have been camera issues reported on S21 series not universal and not had this issue on an S21 Ultra. Check the Diagnostics as suggested but if no fault detected try other Troubleshooting.
Have you checked your permissions to see all is ok there/ Apps-Camera-Permissions. Are on you the latest camera update and are you able to Reset the camera, via Settings- Reset Settings in the app. An idea to Force stop via Apps-Camera and then clear cache via storage-Clear Data and cache.
could also try in Safe Mode in case conflict with 3rd party apps themes,if ok there would pinpoint recent apps which have been installed.
https://www.samsung.com/uk/support/mobile-devices/how-to-start-my-galaxy-device-in-safe-mode/If no resolution advisable to wipe the cache partition to clear temporary cache files as sometimes these files can be outmoded or even corrupt, data is intact.
1. Turn off the device.
2. Connect To Computer or other Device, TV USB. Press and hold the Volume Up key and then press and hold the Power key
3. When the Android logo displays, release both keys.
4. An 'Installing system update' message will show for 30 - 60 seconds before the Android system recovery menu options appear.
5. Press the Volume down key several times to highlight wipe cache partition.
6. Press Power key to select.
7. Press the Volume down key to highlight yes, them and press the Power key to select.
8. When the wipe cache partition is complete, Reboot system now is highlighted.
9. Press the Power key to restart the device.
If there are still issues need to consider options. Could send an Error Report,Go to Samsung Members-Support-Send Feedback—Camera and ensure that the system logs are attached.
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.