Created attachment 192204 [details]
Full bug report

Steps to Reproduce:

Log into Plasma 6.6.4 Wayland session
Open Application Menu (Kickoff)
Look at bottom of menu where power action buttons should be

Observed Result:
The bottom section of the menu has empty space reserved where the four action buttons should be, but no buttons rendered. Issue affects only certain user accounts on the same system.
Expected Result:
Suspend, Hibernate, Reboot, Shutdown buttons present and functional (per the user's systemFavorites configuration).
Software/OS Versions:

OS: CachyOS (Arch-based)
Kernel: 7.0.5-2-cachyos
KDE Plasma: 6.6.4
KDE Frameworks: 6.18.x
Qt: 6.11.0
Display server: Wayland
DE: Plasma (plasmalogin display manager)
Hardware: Lenovo IdeaCentre AIO 24IMB05 (i7-10700T, Intel UHD 630)

Additional Information:
This bug is per-user, not system-wide. On the same machine, same boot, same Plasma version:

User A (older account, customized): buttons missing on every login
User B (newer account, defaults): buttons present and working normally

Extensive diff investigation showed identical configs between affected and unaffected users for:

~/.config/plasma-org.kde.plasma.desktop-appletsrc (kickoff section, systemFavorites)
~/.config/plasmashellrc
~/.config/ksmserverrc
~/.config/powermanagementprofilesrc
~/.config/kdeglobals (no Action Restrictions in either)
~/.config/startupconfigkeys
~/.config/kded_plugins
User-level systemd enabled services list (identical)

Ruled out as causes:

DBus service file packaging — /usr/share/dbus-1/services/org.kde.Shutdown.service and org.kde.LogoutPrompt.service exist and are correct
Service binaries — /usr/bin/plasma-shutdown and /usr/lib/ksmserver-logout-greeter exist
systemd-logind permissions — CanPowerOff, CanReboot, CanSuspend all return yes; CanHibernate returns na (no swap)
KDE Action Restrictions kiosk settings (none set)
XDG_DATA_DIRS (correct, includes /usr/share)
KDE service cache (rebuilt via kbuildsycoca6 --noincremental, no effect)
~/.config/startkderc workaround from bug 481938 (file doesn't exist)
ddcutil delay (tested POWERDEVIL_NO_DDCUTIL=1 in /etc/systemd/user/plasma-powerdevil.service.d/disable-ddcutil.conf, no effect)

Nuclear reset attempt:
Backed up entire ~/.config/plasma-*, ~/.config/plasmashellrc, ~/.config/plasmanotifyrc, ~/.config/ksmserverrc, and ~/.config/kactivitymanagerd* to ~/plasma-backup/. Logged out and back in. Plasma regenerated default configs. Buttons still missing in affected user account. This rules out anything in ~/.config/plasma-* as the cause.
Workaround that works:
systemctl --user restart plasma-plasmashell.service plasma-powerdevil.service
After manual restart, buttons populate correctly until next reboot. Causes full desktop redraw, not acceptable as production solution.
Journal observations during affected user's boot:
17:39:37  systemd: Started KDE Plasma Workspace.
17:39:37  systemd: Started Powerdevil.
plasmashell: D-Bus service not available: "org.kde.ScreenBrightness"
plasmashell: D-Bus service not available: "org.kde.Solid.PowerManagement"
plasmashell: Failed to register with host portal QDBusError(...
            "Connection already associated with an application ID")
[many other KDE services]: Failed to register with host portal QDBusError(...
            "App info not found for 'org.kde.{ksmserver,ActivityManager,kded6,...}'")
Same services run for the unaffected user with no apparent ordering difference, yet only the affected user's plasmashell fails to populate the buttons.
Hypothesis:
Plasmashell appears to cache "no actions available" at startup when SessionManagement/PowerManagement queries return empty during the brief window before powerdevil and portal services are fully registered. The cache is never refreshed, even when services later become available. Why this manifests for some user accounts and not others on identical configurations is unclear and points to per-user runtime state outside of ~/.config/plasma-*.
Related bugs:

Bug 481938 (RESOLVED FIXED) — original Plasma 6.0 service file packaging issue
Bug 513595 (RESOLVED WORKSFORME) — similar portal registration errors
Bug 482020 (RESOLVED DUPLICATE of 481938)

This bug differs from those: service files are present, fresh plasma config doesn't fix it, behavior is account-specific on identical systems.