Description of problem:

I booted a Fedora Rawhide KDE Plasma live image Fedora-KDE-Live-x86_64-Rawhide-20221001.n.1.iso https://koji.fedoraproject.org/koji/buildinfo?buildID=2069494 I disabled autologin as the liveuser from sddm on Wayland in System Settings. I logged out of Plasma 5.25.90 from the Application Launcher menu. The sddm background was white after logging out of Plasma. Only the user icon and the password box and button could be seen. Most of the text wasn't visible because it was in white by default in the Breeze Fedora theme.

This problem might be related to the f37-backgrounds-37.0.1-1.fc38 change from png to webp format backgrounds https://koji.fedoraproject.org/koji/buildinfo?buildID=2067636
The png background sddm was using no longer existed. Selecting a webp background in System Settings by Startup and Shutdown > Login Screen (SDDM) > Change Background icon for the Breeze Fedora theme > Load From file > select /usr/share/backgrounds/default.webp
made the default background appear in sddm after logging out.

Version-Release number of selected component (if applicable):
sddm-0.19.0^git20220921.21e965a-1.fc38
f37-backgrounds-37.0.2-1.fc38
kwin-5.25.90-1.fc38
qt5-qtbase-5.15.6-1.fc38

How reproducible:
This problem happened each of a few times I tried it in a VM or on bare metal.

Steps to Reproduce:
1. Boot a Fedora 37 KDE Plasma installation. 
2. Log in to Plasma on Wayland
3. Download Fedora-KDE-Live-x86_64-Rawhide-20221001.n.1.iso https://koji.fedoraproject.org/koji/buildinfo?buildID=2069494
4. Boot Fedora-KDE-Live-x86_64-Rawhide-20221001.n.1.iso in a GNOME Boxes QEMU/KVM VM with 3 GiB RAM and EFI enabled or on bare metal from a USB flash drive written with Fedora Media Writer 
5. Start System Settings
6. Disable autologin from sddm as the liveuser by Startup and Shutdown > Login Screen (SDDM) > Behavior > Remove the check mark for Automatically log in as user liveuser
7. Select Apply
8. Close System Settings
9. Select the Application Launcher menu from the bottom left of the screen
10. Log out of Plasma by Leave > Log out from the Application Launcher menu 

Actual results:
The sddm background was white after logging out of Plasma in a Fedora Rawhide KDE Plasma live image

Expected results:
The sddm background would be the default background after logging out of Plasma in a Fedora Rawhide KDE Plasma live image

Additional info:

Logging out of Plasma to sddm on Wayland sometimes ended up at a text console on a VT instead of sddm due to https://bugzilla.redhat.com/show_bug.cgi?id=2073725 When that problem happened, I needed to reboot and try again.