If I use the command ls -l /dev/ttyACM0 I get this:
crw-rw-rw- 1 root uucp 166, 0 9 ott 00.49 /dev/ttyACM0
so the correct group should be uucp but I tried using the command sudo usermod -a -G uucp $USER and it still doesn't work correctly. (Now there are the right permissions because I used the command sudo chmod a+rw /dev/ttyACM0)