Well i just did the update on my AMD CPU/GPU Laptop with Manjaro/KDE.
All what i did was:
1.Fresh start
2.Log out
3.crtl+alt+f3 to open TTY
4.sudo pacman-mirrors --fasttrack
5.sudo systemctl stop sddm
6.sudo pacman -Syu
and spammed Y to replace everything
7.reboot
Im NOT even deleted ./cache or reseted ./config stuff, on my 4year’s old home user account. I’m not even switched any of my Theme to default, that i downloaded from the KDE Store, everything is still customised, but few icon’s are missing.
Restart from taskbar is working flawless here from the taskbar.
Maybe you need under SDDM Settings, Empty session activate.