I updated my ios to 14.5.1 and my camera and flash light isn't working but when I downgrade it works now Apple unsigned the ipsw 14.4.2 the one that works on my phone I'm stuck to this new version and can't use my phones camera

If the flash isn't working

On an iPhone X or later or an iPad, swipe down from the upper-right corner of the screen. On an iPhone 8 or earlier, swipe up from the bottom edge of any screen. ... If the flash works only sometimes, open the Camera app and tap the flash button to choose a different setting.

If the camera or flash on your iPhone, iPad, or iPod touch isn't ...

iOS once updated cannot be rolled back.

Before updating to the latest iOS 14.5.1 as told in your post what was your earlier iOS version. Then you can look into the iOS changes that have happened between the earlier version on your iPhone and this new version that you have updated now. 

This will give you a broader idea of the issue if it is directly linked to the iOS version or is triggered by something else.