The file picker is working for me. see screenshot
My only issue is that the file picker always comes up on the laptop screen instead of the external screen like the previous file picker. I’ll probably go back to the other one because of this issue unless there’s a tweak for this.
I got it. Had to set the rule “Ignore requested geometry” to Force = yes
Is this button on for you? see screenshot
I changed my file picker back. The KDE picker does not filter as you type when looking for something. MAJOR NO GO for me.
Hello, I stumbled upon this thread after having the same issue in firefox in OpenSUSE. I followed all the recommendations above and nothing helped, I was in the same status as txtechnician.
In the end, I found that the way to fix it was to remove the “kmozillahelper” package and restart firefox. Then preview works as expected.
Hi @txtechnician, I have the same problem on my Kubuntu 24.04 and I find the solution is to install gwenview and kio-extras-data and suddenly the image preview and thumbnail for all application and image appear on my desktop in KDE v5. Then you can setup the file extension preview on Dolphin file manager. Gutluck hope it’s can solve your problem. 
