Plasma/KDE has this with the kreadconfig5 and kwriteconfig5 commands, and it uses a simple INI-like format: https://userbase.kde.org/KDE_System_Administration/Configura...

GNOME has the gsettings command for this, which is the equivalent of the `defaults` command in macOS. Many guides still refer users to the `dconf` command, though, which is technically a lower-level tool but basically does the same thing for 99.999% of GNOME installations. (Users/distro-makers can actually choose the storage format on GNOME's case.)