Created attachment 177002 [details]
An image of the greyed-out preview panel button. You can also see an icon where there should be a preview.

SUMMARY

Using the latest Krita currently available on the Ubuntu repository & with file previews enabled in the native (KDE Plasma) file picker, Krita will not display previews for any file. Furthermore, the preview panel option in the far left dropdown menu where one might also enable viewing the bookmarks button or hidden files is also greyed out & inaccessible.

When run via terminal, it produces the following record:

kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found
kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found
kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found
kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found
kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found
kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found
krita.lib.widgetutils: KoFileDialog::onFilterSelected: Cannot find suffix for filter "*.kra *.pdf *.exr *.krz *.krz *.kpp *.avif *.bmp *.dib *.gif *.heic *.heif *.jp2 *.jpg2 *.jpg *.jpeg *.jpe *.jfif *.jp2 *.jpg2 *.jp2 *.jpg2 *.jpf *.jpx *.jxl *.ora *.psd *.png *.svg *.tif *.tiff *.psd *.ico *.webp *.exr *.gbr *.vbr *.gih *.jp2 *.jpg2 *.bay *.bmq *.cr2 *.crw *.cs1 *.dc2 *.dcr *.dng *.erf *.fff *.hdr *.k25 *.kdc *.mdc *.mos *.mrw *.nef *.orf *.pef *.pxn *.raf *.raw *.rdc *.sr2 *.srf *.x3f *.arw *.3fr *.cine *.ia *.kc2 *.mef *.nrw *.qtk *.rw2 *.sti *.rwl *.srw *.psd *.pbm *.pgm *.ppm *.psb *.psd *.r16 *.r32 *.r8 *.tga *.icb *.tpic *.vda *.vst *.xbm *.xcf *.xpm *.csv"
kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found
kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found
kf.service.services: KServiceTypeTrader: serviceType "ThumbCreator" not found

I was led to believe that my kio-extras install might have been damaged, but reinstalling it didn't improve matters.

It may also be worth noting that I had to manually install qt5-image-formats-plugins to get Krita to render thumbnails for webp images within the program itself (i.e. on the startup screen's "Recent Images" window).

STEPS TO REPRODUCE
1. Open Krita.
2. Open a file dialog of any sort.
3. Witness the terminal output (if open) & otherwise marvel at the absence of thumbnails.

OBSERVED RESULT

Icons instead of previews.

EXPECTED RESULT

Previews instead of icons.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Kubuntu 24.10 / KDE Plasma 6.1.5
KDE Plasma Version: 6.1.5
KDE Frameworks Version: 6.6.0
Qt Version: 6.6.2

ADDITIONAL INFORMATION

None, really.