Comment # 4 on bug 1002865 from Wolfgang Bauer

(In reply to Andreas Bock from comment #2)
> I tried all available selections icewm, twm, kodi kde5, kde plasma : they
> all bevave the same. After I enter the password I get that black screen with
> mouse.

Hm, that's strange.
Then it's rather not a problem with all those desktops...

Reminds me of bug#997294 though.
Does the desktop appear if you press Ctrl+Alt+F1 (to switch to a text mode
console) and then Ctrl+Alt+F7 to switch back?

> Some googling showed me that:
> https://bugs.kde.org/show_bug.cgi?id=358171

Well, it doesn't sound exactly like your problem, but it may have a similar
root (intel's SNA acceleration).

So, does it work if you switch to a different sddm theme?
E.g. set Theme=maui in /etc/sddm.conf.

Are you using intel?
If yes:
Does it help to switch to the older (but more stable) UXA acceleration?
https://en.opensuse.org/SDB:Switch_xf86-video-intel_to_UXA

You may also try to disable the intel driver completely by adding "nomodeset"
to the boot options (press 'e' at the boot menu and append "nomodeset" to the
line starting with "linux" or "linuxefi", then press F10 to boot, this way it
will only apply to the current boot and not permanently alter your system).

Also maybe try to use the generic "modesetting" driver too, by just
uninstalling xf86-video-intel. ("modesetting" will still use intel's OpenGL
hardware support so you shouldn't loose much, actually it's reported to be more
stable and even faster on some intel systems at least)

The latter two suggestions would also apply to other (open source) drivers like
nouveau or radeon (of course you should uninstall xf86-video-nouveau or
xf86-video-ati then, not xf86-video-intel).

> Seems that bug was build in again?

That bug was never fixed in Plasma/the breeze theme, as it was (is?) a bug in
the intel graphics driver.

intel didn't release a new driver in years though AFAIK, so distributions
started shipping random git versions, that may have random bugs too.

> But as root I can use breeze theme and
> all works fine with the desktop

Well, it's not a general problem with the breeze theme, it only happens with
sddm as I understand it.

So the question is if you can login via sddm as root...
Root login is disabled by default though, you'd have to set MinimumUid=0 in
/etc/sddm.conf (this will display all system users too though, Plasma 5.8's
sddm theme will have an option to manually enter the user name as well).
I suppose you will have the same problem then as when logging in as user.