Can anybody tell me what should be inside .kde4/share/apps?

Desktop Environments Plasma
1

I think some folders are missing and causing problems while installing themes.

2

~/.kde4 is not present in a clean, new install of KDE Plasma 5.23.3. Is it possible you’ve installed some (old) theme that may have brought the .kde4 folder in?

While installing stuff from the KDE Store, do look at the age of the package.

3

I have been using kde since 5.21. What will happen if I reinstall it?

4

What’s in the directory? Is it just empty? If it’s an empty directory with nothing in it, nothing will happen.

If you reinstall it? I’m not following. Arch doesn’t exist in the past. It’s always now. By installing something from yesterday is futile usually, add next update is gone again.