SUMMARY
I use Kate (rpm version now, as flatpak doesnt work view preview) together with the preview plugin using Okular. 
When creating a .md file manually, the document preview plugin doesnt render it as markdown, probably because the mimetype of the generated document isnt adapted to the file extension. This may also be a problem with other mimetypes.


STEPS TO REPRODUCE
1. Add the Preview Plugin to Kate and enable the view
2. Create a new document, save it as document.md
3. write some markdown syntax like "## header"
4. reload the document preview

OBSERVED RESULT
The mimetype seems to be incorrect. The preview plugin works normally on files created through Dolphin through templates or by creating a text file and naming it "document.md" manually

EXPECTED RESULT
Kates created documents should inherit the mimetype from their extension. I guess

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 37
KDE Plasma Version: 5.27.0
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8
Kernel Version: 6.1.13-200.fc37.x86_64 (64-bit)
Graphics Platform: Wayland