SUMMARY
During the start of a x11 session, kwin cannot start the plasma session.

STEPS TO REPRODUCE
1. log-in in sddm
2. Wait until it works. But it stays forever, without having the kernel to freeze.

OBSERVED RESULT
The gear of the login screen spins and it doesn't arrive to the plasma screen. The kernel is still responsive: you can kill X11 and start again, with the same result. The ssh is fine. The mouse appears and can move. Just KDE is not usable (no alt+f1 nor alt+f2), no display (it is black with the gear still on).
Clearing the kde config files didn't help.

The end of .xsession-errors gives:
kdeinit5: opened connection to :0
org.kde.plasma.session: process job  "kcminit_startup" finished with exit code  0
kf.coreaddons: "Could not load plugin from notificationhelper: The shared library was not found."
kf.coreaddons: "Could not find plugin kded_notificationhelper"
kf.kded: Could not load kded module "notificationhelper":"Could not find plugin kded_notificationhelper" (library path was:"notificationhelper")
Warning: Setting a new default format with a different version or profile after the global shared context is created may cause issues with context sharing.
FATAL ERROR: KWin could not find the KWinX11Platform plugin


EXPECTED RESULT
Plasmashell to appear.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: kubuntu 22.04.
KDE Plasma Version: 5.24.4
Using the proprietary nvidia drivers.

Result of the kwin-x11 version:
Package: kwin-x11
Version: 4:5.24.4-0ubuntu1
Priority: optional
Section: universe/kde
Source: kwin
Origin: Ubuntu
Maintainer: Kubuntu Developers <kubuntu-devel@lists.ubuntu.com>
Original-Maintainer: Debian Qt/KDE Maintainers <debian-qt-kde@lists.debian.org>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 1 451 kB
Provides: kwin, x-window-manager
Depends: kwin-common (= 4:5.24.4-0ubuntu1), libc6 (>= 2.34), libepoxy0 (>= 1.0), libgcc-s1 (>= 3.4), libkf5configcore5 (>= 5.90.0~), libkf5configgui5 (>= 5.90.0~), libkf5configwidgets5 (>= 5.90.0~), libkf5coreaddons5 (>= 5.90.0~), libkf5crash5 (>= 5.90.0~), libkf5globalaccel-bin, libkf5globalaccel5 (>= 5.90.0~), libkf5i18n5 (>= 5.90.0~), libkf5notifications5 (>= 5.90.0~), libkf5plasma5 (>= 5.90.0~), libkf5quickaddons5 (>= 5.26.0), libkf5service-bin, libkf5service5 (>= 5.90.0~), libkf5windowsystem5 (>= 5.90.0~), libkwaylandserver5 (>= 5.24.4), libkwaylandserver5-5.24, libkwineffects13 (= 4:5.24.4-0ubuntu1), libkwinglutils13 (= 4:5.24.4-0ubuntu1), libkwinxrenderutils13 (= 4:5.24.4-0ubuntu1), libqaccessibilityclient-qt5-0 (>= 0+git20130108), libqt5core5a (>= 5.15.1), libqt5dbus5 (>= 5.15.0~), libqt5gui5 (>= 5.15.0~) | libqt5gui5-gles (>= 5.15.0~), libqt5qml5 (>= 5.15.0~), libqt5quick5 (>= 5.15.0~) | libqt5quick5-gles (>= 5.15.0~), libqt5widgets5 (>= 5.15.0~), libqt5x11extras5 (>= 5.15.0~), libstdc++6 (>= 11), libx11-6, libxcb-composite0, libxcb-keysyms1 (>= 0.4.0), libxcb-randr0 (>= 1.3), libxcb-render0, libxcb-shape0, libxcb-xfixes0, libxcb1 (>= 1.6), libxi6 (>= 2:1.5.99.2)
Breaks: kwin-common (<< 4:5.20.4-4~)
Replaces: kwin-common (<< 4:5.20.4-4~)
Homepage: https://projects.kde.org/projects/kde/workspace/kwin
Task: kubuntu-desktop, ubuntustudio-desktop-core, ubuntustudio-desktop
Download-Size: 417 kB
APT-Manual-Installed: yes
APT-Sources: http://fr.archive.ubuntu.com/ubuntu jammy/universe amd64 Packages
Description: KDE window manager, X11 version
 KWin (pronounced as one syllable "kwin") is the window
 manager for the KDE Plasma Desktop. It gives you complete
 control over your windows, making sure they're not in the way
 but aid you in your task. It paints the window decoration,
 the bar on top of every window with (configurable) buttons
 like close, maximize and minimize. It also handles placing
 of windows and switching between them.
 .
 This package is part of the KDE base workspace module.