Using TW has been a nightmare trying to find out from different sources what “extra” software I need to configure KDE. I still have no thumbnails in dolphin. All I get are icons of pictures, texts etc. I have tried looking in several places for preview checkboxes in dolphin in the applications menu, context menus and other places. I have loaded all the thumbnail software available in the one-click area. Still no thumbnails. Can anyone tell me how to get thumbnails in dolphin like other versions of KDE from Manjaro or Neon or even (God-forbid) the gnome desktop does? Thank you.
Hi
Hmmm, GNOME works OOTB 
I guess I can try and help, is kio-extras5 installed, that seems to be the one that has thumbnailers…
Thank you for the help. No it’s not installed. I installed it and rebooted, alas, still no thumbnails. I’ll keep trying.
Hi
Can you create a test user and login as that test user, does the the thumbnail function work? If so then it’s as your user, probably a config file needs moving/deleting…
making a test user does work. What then do I do? thanks for your help!!
Hi
Hopefully a Forum Plasma user will advise more… but at least identified
Means dolphin’s settings is enabled by default.
Why not go to the dolphin settings and in the preview click the default.
If that doesn’t work you may check ~/.config/dolphinrc
The preview settings here (15.2) are this:
[PreviewSettings]
Plugins=imagethumbnail,jpegthumbnail,kraorathumbnail,opendocumentthumbnail,directorythumbnail,gsthumbnail,rawthumbnail,svgthumbnail,textthumbnail,ffmpegthumbs
You can compare the working / non-working settings of your both users. Any differences?