I had a problem. Linux mentality is to use ROOT account only when needed, not in every day use. I had to use ROOT account with arduino ide because I couldn’t upload sketch with normal user account. After several years I did manage to do something about it.
I did find same advice several times, but adding my user name to dialout group did not help. This is from arduinos own page.
sudo usermod -a -G dialout <username>
After long googling I did find a solution. Old setting file. I have updated arduino IDE several times over the years and because I use ubuntu, my home directory has followed me years and over multiple computers. I don’t know what was the reason inside of file, but deleting .arduino/preferences.txt did work! (As instructed here.)
Close arduino IDE before deleting! IDE will ask questions when you start it next time, but at least my in case it started working!
Edit: Also be warned that from ubuntu repositorys you get old version of arduino ide. Download it from arduino.cc pages!