I have upgraded to 20.04. Arduino IDE loaded with:
snap install arduino
as suggested (version 1.8.13). The port selection item cannot be selected. As suggested in other posts, I have done:
sudo usermod -a -G dialout $USER
Actually, this added dialout in groups. I rebooted, dialout is still in groups, but still the port cannot be selected and, of course, I cannot upload anything on Arduino.
The problem seems to be solved. The snap installation was not successful.
I went through the distro from Arduino, and found a nice file: arduino-linux-setup.sh. I have run install.sh as root, then:
arduino-linux-setup.sh $USER
as regular user and finally ports are visible and can be used.
I could not find any place where this procedure is suggested, not even from the Arduino web site, although they had for sure defined what is in arduino-linux-setup.sh.
I hope this is useful and will help also to solve problems for future distro.