I have openSuse Leap 15.4 with three user accounts. The KDE problems are only with a specific user. Problems first started showing up with evolution when messages could not be displayed because "something went wrong ............". Then applications started taking a very long time to start up or maybe they don't start up at all. Sometimes Firefox starts up after a very long time. LibreOffice, Kate, not starting at all. When I log in as this specific user on GNOME, LXDE etc all these applications start up fast and work fine.

When I log into KDE as one of the other users everything works fine. After doing some Google searches on this problem I tried renaming my ~/.kde4 directory and then rebooting and then doing a KDE login but it didn't change anything.

Also, forgot to mention that I am now unable to logout using the "logout" icon from KDE menu. The only way I can log out is to choose reboot or shutdown, then choose logout
from the menu that follows.

One thing that immediately comes to mind is that the home space allocated to that user is full or has only little space left.

This is my personal computer on which I have 3 separate user accounts set up and used.
I have never setup/used any kind of user disk space quota configurations on this computer.

Right now when running Plasma for this particular user I can start up the main menu and
select an application but nothing will start up. The only way I can log out is by using
"CTRL-ALT-BACKSPACE" 3 times.

Operating System: openSUSE Leap 15.4
KDE Plasma Version: 5.24.4
KDE Frameworks Version: 5.90.0
Qt Version: 5.15.2
Kernel Version: 5.14.21-150400.24.21-default (64-bit)

The partition I have mounted on /home has about 17 G of space
of which about 9.9 G or 60% is being used.
Of that, about 4.7 G is being taken by the user who cannot use Plasma.

This may be an issue with 'admin' versus 'normal' users rights. Can you confirm if all users are bestowed with the same rights? You can check this in System Settings ... User Manager. Also, the user "who cannot use plasma" will likely not be able to use sudo (this varies from distro to distro, so I it is just a guess).

The other likely issue is corrupt Plasma configs and local directories. Assuming fred is your problem user, you might set aside these directories using a virtual terminal (Ctrl + Alt + F2, sign in as fred). Do not sign into Plasma when doing this:

for _dir in .config .local; do
mv "/home/${_user}/${_dir}" "/home/${_user}/${_dir}.old";
done

You can always move these back in part or in whole after you test. Then press Ctrl + Alt + F1 and sign into Plasma as Fred and see if it works.

I apologize if this is too basic. Good luck!

I did this renaming (moving) of the .config and .local directories and it seemed to solve the problem.
Then I tried doing each one separately by itself and found out that some file(s) inside .config must
be the problem. Apparently, no problem with .local.

When doing this, some information related to evolution and libreoffice writer is lost.
Upon logging into Plasma, new files are created inside .config and then when starting
up evolution, it tells me I'm using evolution for the first time and asks me to set up a new
account. When using Writer and opening a file, there is no option for "Recent Documents".
Kate is unaffected. Looks like this information for Kate is somewhere in .local.

What I probably should do: move existing .config to .config.old, restart Plasma, copy the contents
of .config.old/evolution and .config.old/libreoffice/4/user over to these newly created directories
in .config. These applications probably would have to be started up a first time so that all these
subdirectories are created. Evolution may have a tool for importing some files from .config.old/evolution.

> What I probably should do: move existing .config to .config.old, restart Plasma, copy the contents
of .config.old/evolution and .config.old/libreoffice/4/user over to these newly created directories
in .config. These applications probably would have to be started up a first time so that all these
subdirectories are created. Evolution may have a tool for importing some files from .config.old/evolution.

What I normally do is use Meld or Kdiff3 between the old an new directories. I do this without the apps running to avoid corruption:

meld .config.old .config

Then merge over the data from left to right. I'm always careful to merge from right to left, as this can break your backup. Generally, I only merge over configs and data I'm certain I want restored. I recommend the same for .local, as this will have local data that may be valuable for apps like evolution:

meld .local.old .local

Once you get it all working again, you can removed the *.old files, but I recommend you set them aside for a few days before doing that.

I hope that helps!

I used:
meld .config.old/evolution .config/evolution
and
meld .config.old/libreoffice/4/user .config/libreoffice/4/user

I was unsure how to use it at first. When you right click on a file in the .old directory
it gives you an option to copy it over to the other directory which is what I did. The
evolution directory in .config.old had a lot of files that didn't exist in the new evolution
so I just used meld to copy them over. Also, any old file that was larger than the new
was copied over.

The "Recent Documents" info for libreoffice writer is in registrymodifications.xcu so I
just used meld to copy this file from the old to the new directory.

Plasma seems to now be operating OK for this user and also evolution and libreoffice.

Many thanks for the advice.

Thanks for the help and advice.