To make sure: Selfie camera works, rear (main) camera does not work, right?
One easy first thing to check is whether using a different camera app (e.g. Open Camera) makes a difference. Given the flashlight doesn’t work either, it’s unlikely to make a difference, but it doesn’t hurt to try.
If using a different app does not change anything, you might want to check if the camera module is properly connected:
Please note that the Rear Camera Module connector (the black thing bearing the empty triangle icon) can sometimes become disconnected on its other, “invisible” end, too – beneath the camera icon that you can see in Step 11.
P.S.: Welcome to the Community Forum! 