Hi @AS64, let me see if I can help out here!
Have you been able to carry out a quick test of the camera to see if the hardware works as intended? To do this, find and tap Settings > Support > Xperia Tests > Camera/Front camera.
Another thing that you can try is to clear the data for the camera app. This will not erase any previously taken photos, but it will reset all settings for the app which might do the trick. Find and tap Settings > Apps & notifications > App-info > Camera > Storage > Clear data > Tap "OK" > Restart the phone.
If that does not help, I would suggest that you try is to reboot your phone in safe mode to see if you are able to open the camera app there. Safe mode is a troubleshooting mode where all apps downloaded from Play Store is temporarily deactivated and by entering this mode, you can see if this behaviour is caused by a downloaded app. For more information on safe mode and how to use it, click here.
If the camera behaves the same way in safe mode, I would suggest that you try to repair the software using a computer and Xperia Companion. Keep in mind though that a software repair will erase all user data from the phone, so make sure to do a backup of your user data before the repair.
Try these measures and feel free to keep me posted with the results!
