After a Neon install, I found this file: /etc/sudoers.d/10-installer with the following contents: %sudo ALL=(ALL) ALL 1) It was overriding the 'sudo' group line in /etc/sudoers (causing me all kinds of confusion) 2) dpkg -S said it didn't know who owned the file. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Latest Neon ISO at time of install: neon-user-20241201-0744.iso