No pictures shown with Digikam 9.1.0 and Kubuntu 25.10

[Jens Schwarzhaupt]

Dear Digikam Developers :),

I recently switched from Windows to Linux and as photography is one of my 
hobbies, I decided to contribute to Digikam even if I've never developed an 
application SW before. At least I have some ideas coming from a very powerful 
windows tool :)

Currenty I'm working as a systems engineer for product safety for power 
electronics but in the past I also worked as a SW-developer for embedded 
systems where I mainly used C for around 5 years. Besides of that I do 
scripting (perl, python, java) here and there and a some smart home stuff if 
there is some free time between family and work. So I think I could be able to 
contribute :)

To start developing I set up a clean install of Kubuntu 25.10, installed QT 
6.10.2 via the QT installer incl. dependencies and finally used kde-builder to 
build the latest version of Digikam. And - suprise - Digikam 9.1.0 is running. 
But unfortunately I can not open/show pictures.

I added a picture folder in my home directory as a new collection and the 
preview pictures are shown, I can tag them, filter, search... all is working. 
But if I try to open a picture (e.g. double click), I only get a message in 
the main window "Bild kann nicht geladen werden" ("Can not load picture"). 

The terminal says the following if I try to open a picture (the Epson is my 
printer that is automatically detected by Kubuntu):
digikam.dimg: ICM Wayland: the device is not a screen: "/org/freedesktop/
ColorManager/devices/cups_EPSON_ET_8550_Series"
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::begin: Paint device returned engine == 0, type: 2

At the moment I don't even know whether this is a fault message or not but I 
assume that showing pictures should work with V 9.1.0 even if it's in 
development. At least I would prefer to start with a baseline for which the 
core functions are working...

Can you give me some advice where I coud start troubleshooting? Is it Kubuntu? 
Is it the build with kde-builder? Is there some better platform to discuss 
such topics?

What I already did, was to build V9.0.0 with the tag option of kde-builder but 
the result was the same.

Looking forward for your replies! 

Regards,

Jens