SUMMARY
Pinning apps to the task manager is not persistent. It is not saved. 

Manually editing ~/.config/plasma-org.kde.plasma.desktop-appletsrc the include pinned apps does still work. However, it seems the file is updated on the fly as expected. 

Potentially notable details for my system config: init=runit; wayland ; no explicitly installed X

Issue is unresolved, but seems similar to this resolved post:
https://bugs.kde.org/show_bug.cgi?id=474228
and this closed post:
https://bugs.kde.org/show_bug.cgi?id=431857

STEPS TO REPRODUCE
1. Start with clean system, Wayland used, only X packages being xorg-common & xorg-server-xwayland
2. Pin apps to the Icons-Only Task Manager
3. Logout or reboot
4. Login

OBSERVED RESULT
Pinned apps are not saved

EXPECTED RESULT
Pinned apps are saved and reproduced upon subsequent logins

SOFTWARE/OS VERSIONS
Operating System: Void Linux (glibc)
Kernel Version: 6.6.32_1 (64-bit)
KDE Plasma Version: 6.0.5
KDE Frameworks Version: 6.2.0
Qt Version: 6.6.32_1 (64-bit)
Graphics Platform: Wayland

ADDITIONAL INFORMATION
[Hardware]
Processors: 32 × AMD Ryzen 9 5950X 16-Core Processor
Memory: 62.7 GiB of RAM
Graphics Processor: AMD Radeon RX 6950 XT

[Explicitly installed packages in order of install]
[utils and repos] snapper bottom curl ntfs-3g nerd-fonts void-repo-multilib{,-nonfree} void-repo-nonfree wget xtools xz 
[system setup] socklog-void cronie apparmor chrony runit-nftables NetworkManager 
[session management] elogind libelogind dbus-elogind dbus-elogind-libs polkit-elogind
[drivers] mesa-dri vulkan-loader mesa-vulkan-radeon mesa-vaapi mesa-vdpau 
[wayland & plasma] kde5 kde5-baseapps qt6-wayland-tools wayland-protocols wayland-utils Vulkan-Tools plasma-wayland-protocols glfw

[enabled services]
[defaults] dbus socklog-unix cronie chronyd elogind nftables NetworkManager sddm snapperd bluetoothd