There's no visible way to remove custom commands from the custom commands module configuration. There's neither a context menu, nor a visible remove button, neither does the Delete button on the keyboard work. To remove an entry you need to clear both input fields and after clicking OK the entry disappears. Reproducible: Always
Hello from KDE's bug team! The KDE Connect page in System Settings was recently removed, in favor of a new standalone app used to configure KDE Connect. As such, this Bugzilla ticket is no longer relevant due to the software it's about no longer existing. Please open new bug reports for the desktop ap at https://bugs.kde.org/enter_bug.cgi?product=kdeconnect&component=desktop-application. Thanks!