It sounds a little like the camera may not be available or there's a bug in the camera app.
I would do these two things...
Go into Settings to the Camera app, Settings>Applications>Camera (it may be a system app so you might have to choose an option to display system apps if it doesn't appear in the list at first. Look in a menu for display/show system apps.)
Clear the cache and data for the camera. (You may have to switch to the storage page to find these options.)
Go to your Permission manager. It should be close to your Applications page in Settings. It may be part of that page, check the menu for Applications.
Remove camera permission for all apps. Go into Camera permissions and remove all of the applications you see there. This is only temporary, as each app will request permission when it is opened or needs to use the camera again. It'll be like opening the app for the first time.
Before opening any other apps, after taking the above steps, open the Camera app and see if the icon has returned.
Let us know your findings.
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