KDE application icon not displayed in Ubuntu

Some icons are missing from a KDE application (Okular) in Ubuntu.

How could this be fixed?

Opening okular from terminal shows:
android@android:~$ okular
Invalid Context= "Apps" line for icon theme:  "/snap/communitheme/current/share/icons/Suru/256x256@2x/apps/"
Invalid Context= "Mimetypes" line for icon theme:  "/snap/communitheme/current/share/icons/Suru/256x256@2x/mimetypes/"
Invalid Context= "Mimetypes" line for icon theme:  "/snap/communitheme/current/share/icons/Suru/scalable/mimetypes/"
Invalid Context= "Apps" line for icon theme:  "/snap/communitheme/current/share/icons/Suru/256x256@2x/apps/"
Invalid Context= "Mimetypes" line for icon theme:  "/snap/communitheme/current/share/icons/Suru/256x256@2x/mimetypes/"
Invalid Context= "Mimetypes" line for icon theme:  "/snap/communitheme/current/share/icons/Suru/scalable/mimetypes/"

Solution 1:

First install qt5ct:

sudo apt install qt5ct

Then run it and choose your preferred icon/theme:

Finally set QT_QPA_PLATFORMTHEME to qt5ct in your .profile:

echo 'export QT_QPA_PLATFORMTHEME=qt5ct' >> $HOME/.profile

Re-login and it should fix the issue.