I've had a slew of updates this afternoon, including an upgrade to Cinnamon 4.4.4, a new kernel (5.4.5-1-MANJARO) and a downgrade to Systemd 2.4.2. After applying the updates, desktop icons failed to load, and no new icons can be added. (The right click button on the laptop fails to load a menu for wallpaper changes, etc.) I have an old 6560b Probook, 16GB, SSD and so on. Any help would be appreciated.
So, you are on testing or unstable, as me, but i can't confirm the issue you have. That means it might be something on your end. Make sure you have the system fully updated and did not ended up with a partial update.
sudo pacman-mirrors -f5 && sudo pacman -Syyu
you can do that from TTY if the desktop fails to load.