And this is the same issues reported for ArchLinux:
However, I have tried the solution suggested (switching Display manager
from SDDM to LighDM) and it did not work for me at all.
I also found this same issue reported on OpenSUSE forum. You can find
more reports by running Google search for the error message string:
"Layout changes must be applied before other changes cam be made."
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KDE workspace broken after update to Plasma 5.12
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