The login screen of SDDM doesn’t show virtual keyboard nor keyboard layout switcher, I filled the bug to KDE but what they concluded is that Manjaro ships wrong or corrupted package.
See 426117 – SDDM login screen is missing virtual keyboard, keyboard layout changer, and battery icon for more details.
Operating System: Manjaro Linux
KDE Plasma Version: 5.19.5
KDE Frameworks Version: 5.73.0
Qt Version: 5.15.0
Kernel Version: 5.8.6-1-MANJARO
OS Type: 64-bit
This might help