Here some entries from an sddm start in /var/log/syslog, filtered by grep sddm:
Oct 18 08:46:21 betty sddm[925]: Initializing...
Oct 18 08:46:21 betty sddm[925]: Starting...
Oct 18 08:46:21 betty sddm[925]: Logind interface found
Oct 18 08:46:21 betty sddm[925]: Adding new display on vt 7 ...
Oct 18 08:46:21 betty sddm[925]: Loading theme configuration from ""
Oct 18 08:46:21 betty sddm[925]: Display server starting...
Oct 18 08:46:21 betty sddm[925]: Adding cookie to
"/var/run/sddm/{aa4bb32b-dbfe-438e-8bde-4348c400857f}"
Oct 18 08:46:21 betty sddm[925]: Running: /usr/bin/X -dpi 0 -auth
/var/run/sddm/{aa4bb32b-dbfe-438e-8bde-4348c400857f} -background none -noreset
-displayfd 17 -seat seat0 vt7
Oct 18 08:46:22 betty sddm[925]: Setting default cursor
Oct 18 08:46:22 betty sddm[925]: Running display setup script
"/usr/share/sddm/scripts/Xsetup"
Oct 18 08:46:22 betty sddm[925]: Display server started.
Oct 18 08:46:22 betty sddm[925]: Socket server starting...
Oct 18 08:46:22 betty sddm[925]: Socket server started.
Oct 18 08:46:22 betty sddm[925]: Loading theme configuration from
"/usr/share/sddm/themes/breeze/theme.conf"
Oct 18 08:46:22 betty sddm[925]: Greeter starting...
Oct 18 08:46:22 betty sddm-helper[1386]: [PAM] Starting...
Oct 18 08:46:22 betty sddm-helper[1386]: [PAM] Authenticating...
Oct 18 08:46:22 betty sddm-helper[1386]: [PAM] returning.
Oct 18 08:46:23 betty systemd[1388]: Cleanup lingering KCrash metadata was
skipped because of a failed condition check
(ConditionPathExistsGlob=/var/lib/sddm/.cache/kcrash-metadata/*.ini).
Oct 18 08:46:23 betty systemd[1388]: Cleanup lingering KCrash metadata was
skipped because of a failed condition check
(ConditionPathExistsGlob=/var/lib/sddm/.cache/kcrash-metadata/*.ini).
Oct 18 08:46:23 betty systemd[1]: Started Session 1 of User sddm.
Oct 18 08:46:23 betty sddm[925]: Greeter session started successfully
Oct 18 08:46:23 betty sddm-greeter[1408]: High-DPI autoscaling not Enabled
Oct 18 08:46:23 betty sddm-greeter[1408]: Reading from
"/usr/share/xsessions/plasma.desktop"
Oct 18 08:46:23 betty sddm-greeter[1408]: Loading theme configuration from
"/usr/share/sddm/themes/breeze/theme.conf"
Oct 18 08:46:23 betty sddm-greeter[1408]: Connected to the daemon.
Oct 18 08:46:23 betty sddm[925]: Message received from greeter: Connect
Oct 18 08:46:23 betty sddm-greeter[1408]: QFont::fromString: Invalid
description '(empty)'
Oct 18 08:46:23 betty sddm-greeter[1408]: Loading
file:///usr/share/sddm/themes/breeze/Main.qml...
Oct 18 08:46:23 betty sddm-greeter[1408]: QObject: Cannot create children for a
parent that is in a different thread.#012(Parent is
QGuiApplication(0x7fffced42270), parent's thread is QThread(0x55c623077060),
current thread is QThread(0x55c62319ad10)
Oct 18 08:46:23 betty sddm-greeter[1408]: QObject: Cannot create children for a
parent that is in a different thread.#012(Parent is
QGuiApplication(0x7fffced42270), parent's thread is QThread(0x55c623077060),
current thread is QThread(0x55c62319ad10)
Oct 18 08:46:23 betty sddm-greeter[1408]: QObject: Cannot create children for a
parent that is in a different thread.#012(Parent is
QGuiApplication(0x7fffced42270), parent's thread is QThread(0x55c623077060),
current thread is QThread(0x55c62319ad10)
Oct 18 08:46:23 betty sddm-greeter[1408]: QObject::installEventFilter(): Cannot
filter events for objects in a different thread.
Oct 18 08:46:23 betty dbus-daemon[674]: [system] Activating via systemd:
service name='org.freedesktop.UPower' unit='upower.service' requested by
':1.34' (uid=115 pid=1408 comm="/usr/bin/sddm-greeter --socket
/tmp/sddm-:0-PRpPZo")
Oct 18 08:46:23 betty sddm-greeter[1408]: Failed to find a Kirigami platform
plugin
Oct 18 08:46:23 betty sddm-greeter[1408]:
file:///usr/share/sddm/themes/breeze/components/VirtualKeyboard.qml:12:1: Type
InputPanel unavailable
Oct 18 08:46:23 betty sddm-greeter[1408]:
qrc:/QtQuick/VirtualKeyboard/content/InputPanel.qml:127:5: Type Keyboard
unavailable
Oct 18 08:46:23 betty sddm-greeter[1408]:
qrc:/QtQuick/VirtualKeyboard/content/components/Keyboard.qml:38:1: module
"QtQuick.VirtualKeyboard.Plugins" is not installed
Oct 18 08:46:23 betty sddm-greeter[1408]:
file:///usr/share/sddm/themes/breeze/Background.qml:21:5: QML Image: Cannot
open: file:///usr/share/wallpapers/Next/contents/images/5120x2880.jpg
Oct 18 08:46:23 betty sddm-greeter[1408]: Adding view for "HDMI-1" QRect(0,0
1600x1200)
Oct 18 08:46:23 betty sddm-greeter[1408]: Qt Quick Layouts: Polish loop
detected. Aborting after two iterations.
Oct 18 08:46:24 betty sddm-greeter[1408]: Message received from daemon:
Capabilities
Oct 18 08:46:24 betty sddm-greeter[1408]: Message received from daemon: HostName
