Created attachment 142832 [details]
Screen shot of the filters showing empty boxes for the pick flags.

SUMMARY

On Ubuntu 21.10, the flag icons shown in "The DigiKam Handbook" do not display. I get a series of four empty boxes. 

Additionally, if I mark an image as "rejected" nothing displays on the thumbnail (I can't see anything in the documentation showing a whether I should see a "Rejected" pick flag).

STEPS TO REPRODUCE
1. Choose "Filters" tab
2. Open "Labels Filter"

OBSERVED RESULT
Labels filter shows a row of empty boxes where the pick flags should display.

EXPECTED RESULT
I should see flat icons in the pick boxes

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Ubuntu 21.10
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
I'm not sure if I should see flags on images marked as "Rejected." It might be related to this bug, or it might be a separate issue.