By the way, if anyone on any distro wants .kra thumbnails without installing any packages or anything, you can just create a “thumbnailer” file. It’s super-easy!
Just create a simple text file called kra.thumbnailer and paste in the following contents:
[Thumbnailer Entry]
TryExec=unzip
Exec=sh -c "unzip -p \"%i\" preview.png > %o"
MimeType=application/x-krita;
Stick this file in ~/.local/share/thumbnailers and you should be good to go!
(You can also stick it in, e.g. /usr/local/share/thumbnailers, or /usr/share/thumbnailers, etc. Wherever you prefer. These will be a system-wide install, whereas ~/.local/share will only apply to your user.)