KDE 5.20, NVIDIA 455.x, Kernel 5.4 here - the upgrade causes me to be stuck on boot due to a regression in the sddm display manager. Appears to be a race condition, the NVMe drive might be too fast!
Downgrading to sddm 0.18.1 lets me boot to the graphical desktop.
Edit: Fixed with sddm 0.19.0-2.2 - auto login had something to do with it