A neither KDE nor Nvidia user here but from ArchWiki:
To enable support for Wayland in Plasma, also install the plasma-wayland-session package. If you are an NVIDIA user, also install egl-wayland if it is not already installed, and if the session does not start with the proprietary nvidia driver, also enable the DRM kernel mode setting. If that does not work, too, check the instructions on the KDE wiki.
Do you have egl-wayland installed?
If that alone won’t solve the issue, you might need to add:
nvidia_drm.modeset=1
to your kernel parameters (https://wiki.archlinux.org/title/Kernel_parameter).