For disabled people I paste the solution post from page 14:
I've finally solved the problem!
I restored the iPhone 7 Plus with all available iOS versions (13.5, 13.5.1, 14beta1, 14beta2) and no version helped. It was just a waste of time! Apple will probably never fix this problem! Accept that a software update will not help.
I found a way to solve this problem.
First of all, I checked with 3uTools that I had the front camera replaced with a Chinese non-original camera! Apple has killed Chinese replacements parts and to solve the problem you need to replace your front camera with the original part from disassembly!
Step by step list of how to deal with the problem:
1. Install 3uTools (Windows only).
2. Connect iPhone to the computer via cable.
3. On the "iDevice" tab, click "View Verification Report".
4. If the front camera has a different serial number than the one assigned to the motherboard, the program will show the information in red "Front camera may be changed". This means, no less, that in your phone camera has been replaced with a non-original part. Replace the front camera with the original one from the disassembly. However, if the program shows the information in green "Normal" (although this is not possible in my opinion), I do not promise that changing the camera will help something.
5. Look after the original disassembly camera. Search on local auction sites. Do not buy the camera on Aliexpress because you will get the cheapest replacement part there. Even the substitutes have the Apple logo, but of poor graphics quality! Therefore, if you want your front camera to work, try to get the original part. The price of original part is around $ 10 - $ 50.
6. Get the right tools for your phone. You will need: screwdrivers (pentalobe, tri-point Y000 and Phillips), suction cup and spudger. In addition, if you want to remain waterproof, a screen tape will be useful.
However, if you are not good at manual work, go to a technician! Wrong screws can kill your phone's motherboard!
A guide on how to replace the front camera can be found here: https://www.ifixit.com/Guide/iPhone+7+Plus+Front+Camera+and+Sensor+Cable+Replacement/95688
7. No need to restore the phone after replacement front camera.
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