Well funny story Paolombana
We don't really know any solution right now.
If you go trough this thread of answers, you will find some people who have had some form of succes with getting their camera's working again…
You will find some idea's of what could be the problem of our camera's not working, whether it could possibly be hardware or software, but we haven't really figured it out yet.
Right now, I would say that it looks like there is something wrong with Apple their software (MacOS, iOS is for the iPhones, MacOS is for the Macs 😉) but the problem is behind a secure layer, and more deep in MacOS and how it operates.
That means that, unless some of the possible solutions which can be found in this thread end up working for you, we can't really do anything about this right now.
Some of us have been contacted by Apple already and are probably still having talks with them, but for now there isn't really a solution, apart from waiting it out.
I will put some of the troubleshooting tips from this thread down here. These are quite basic, and don't do anything bad to your Mac, but if you have the exact same experience as the rest of us in this thread, these troubleshooting tips won't work for you.
To reset the "SMC" of your Mac: https://support.apple.com/en-us/HT201295
To reset the "NVRAM" or "PRAM" on your Mac: https://support.apple.com/en-us/HT204063
You might also want to try and boot your Mac up into safe mode to see if the problem also is present there: https://support.apple.com/en-us/HT201262
(For safe mode, please note that it is normal that your Mac might work / react a bit slower)
Hope this informs you a bit on the current situation, and if these tips / tricks don't work then I guess…
Welcome to the waiting room ☹️
PS. In your post you say that you updated to the last Sierra update. I do want to ask if you could possibly tell us what OS version you are on (for example 10.15.1), because Apple recently released a update to MacOS with the number 10.15.5
They say in the update notes for this version that it:
"Resolves an issue where the built-in camera may not be detected when trying to use it after using a video conferencing app".
If you are currently on a form of MacOS 10.15, you might want to consider if you want to update to this version, although I want you to know that so far, I don't think I have seen anyone in this thread whose camera started working again after this update.
If you are not on a form of MacOS 10.15 (so for example you are on MacOS 10.14 or 10.13) you might want to try and do some more research on how and if you want to update to 10.15.
PPS. In case you don't know, you can find your MacOS version by going to the top left of your screen, open the top-down menu, and select "About this Mac". Also, you can use this page to help you with that: https://support.apple.com/en-us/HT201260
PPPS. If you try to go to the helpful reply's in this thread, you can see another summary of what we found so far (you can go there when you press on the button above all these messages saying "All replies" and click on "Helpful answers").