SUMMARY
If you try to choose an italic font as the label font, Dolphin will silently not pick the italic option.

STEPS TO REPRODUCE
1. Open Dolphin
2. Configure Dolphin
3. Navigate to View then to one of Icons, Compact, or Details as appropriate
4. Choose Label font: Custom Font then click Choose
5. Pick a font, and choose Font style Italic
6. Click OK
7. Observe file names

OBSERVED RESULT
Filenames are in the chosen font, but are not italic.

EXPECTED RESULT
Filenames are in italic, *or* Dolphin doesn't allow italic to be picked in the font chooser, or Dolphin allows the user to pick italic (if the font chooser cannot be customised) but tells the user that the non-italic version will be used.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20250209
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.2
Kernel Version: 6.13.1-1-default (64-bit)
Graphics Platform: X11

ADDITIONAL INFORMATION
I expect the reason is that italic is used for symbolic links. But, the average user might never come across symbolic links and would be confused if they chose an italic font and had their choice silently overridden.

I also notice that if Underline or Strikethrough is chosen, those are also ignored, so the same applies to them, although I'm sure those would be less likely to be chosen than italic.