Hello.
First Happy new years for everybody.
Now my question.
Is it possible to hide a Bluetooth device knowing its mac address so it does not appear at all.
Any help is welcome.
Hi and Happy New Year to you 
Well if discovery is turned off then it won’t be visible? The paired devices will know about each other but that is it.
Perhaps explain a bit more you use case?
You can disable the device with rfkill so it’s softblocked?
At home, each time I start Bluetooth to copy a file from any home computers to my mobile phone, there is an unknown neighborhood mobile phone which appear. I would like to banned (hide) it.
Hi
It might not be a phone… not sure if you can blacklist, just like wifi hotspots.
Is it trying to pair with your device?
The following command should show you what it is;
hcitool scan --all --flush