When running the LXQt DE,
A new 15.2 install results in the default openSUSE 15.2 wallpaper (dark green with a design to the right which IIRC was the wallpaper for 13.1 approximately).
After some exploration, this is obviously not the intended default wallpaper, and here is the solution…
LXQt Configuration Center > Appearance > Themes
Frost is the default selection which has been the default since 15.1.
Note that unlike 15.1, the “Apply” button has been removed, but now if you select a theme the theme including the wallpaper should be applied dynamically.
You’ll notice that clicking most of the other themes does not change anything.
I found that only if you click on the “System” theme, everything starts working properly.
You can then select “Frost” or any other theme you wish and close to save your setting.
This has been reported to bugzilla.
Don’t know if this is specific to LXQt or any other Desktops.
So for instance I found that KDE seems to explicitly point to the openSUSE wallpaper instead of KDE wallpapers so not seeing a KDE wallpaper by default is different.