I’m probably suggesting the obvious, but have you tried reinstalling plasma-workspace to see if it corrects your problem? I am fully updated and like others here, Autostart is not missing.
it looks like the kcm_autostart on duty for the Autorun section functionality, but somehow in your OS copy it is not indexed/enumerated by KDE settings.
If the package re-installation (and reboot after it) will not help, try to Clean cache to resolve upgrade problems
but do it purely:
-) logout from all active user sessions to sddm (login) screen
-) switch to TTY (Ctrl+Alt+F3) or Fx, where the x is a number from 3 to 6. Textual login screen should appeared
-) enter those 3 commands from Arch wiki
-) systemctl reboot to reboot PC.
If not helped, show us additional info, please:
a)
ls -l -Rh /usr/share/kpackage/kcms/kcm_autostart/
This should not expose your user name as it is expected be `root` by default. My example with listed `Autostart` section in KDE Settings
ls -l -Rh /usr/share/kpackage/kcms/kcm_autostart/
total 24K
drwxr-xr-x 1 root root 4 Oct 24 18:52 contents
-rw-r--r-- 1 root root 8.3K Nov 30 19:19 metadata.desktop
-rw-r--r-- 1 root root 9.9K Nov 30 19:19 metadata.json
/usr/share/kpackage/kcms/kcm_autostart/contents:
total 0
drwxr-xr-x 1 root root 16 Dec 1 20:02 ui
/usr/share/kpackage/kcms/kcm_autostart/contents/ui:
total 8.0K
-rw-r--r-- 1 root root 6.0K Nov 30 19:19 main.qml
b) post textual variant (click “copy” btn) of software section:
Thanks for the hint.
The issue solved by: pacman -Su --overwrite "*" plasma-workspace
(had to add overwrite as it complained reinstalling with failing to (re)write some related files).