As far I see you are using the version 1.0.5 of arduino IDE, I assume that you installed the one in the apt repositories.
You can either try to install one from the snapcraft or the one from arduino's website.
Personally I used the latter one and anything worked like a charm.
Also either the case you can try to loon on Tools->Port if exists a port that is not a /dev/ttyS0 one. Try to play with these options. Finally by searching on dmesg you can find out which port has been located for arduno as well.
Finally an another approach is to unplug your arduino plug it again and type the following command:
dmesg | tail
In order to record the last event as the one that happens when arduino is plugged in to a usb port. The command above will show you the correct port.
For better results you can use the following:
dmesg | tail -f
And continioulsy plug and unplug the arduino from the usp port till you see any arduino related message. The -f parameter allows to show realtime the new logs.