Bug 512830

SUMMARY
I have some big pdfs in one of my directories, and i noticed that my fans went faster when i was in that folder. A quick inspection using htop confirmed it was the preview dolphin was making that was intense for my cpu. So i went to disable the preview, and i expected this to stop. But it didn't.
Each time i open Dolphin, my cpu go to 100% for one core for the same reason, even though the previews of the pdfs weren't showing. The only thing that seemed to solve the issue was to reactivate the preview again, and this time, no more cpu going to 100%.

I should mention that i cleared the Doplhin's cache (~/.cache/dolphin) and ~/.cache/*.kcache files. That didn't helped.

STEPS TO REPRODUCE / OBSERVED RESULT
1. Have a big PDF in a folder and go in it
2. CPU usage should go up to 100% for one core, wait for it to calm down
3. Disable the preview in Dolphin for PDFs
4. Close the settings and go to the folder
5. CPU usage should go up to 100% for one core, wait for it to calm down
6. Close dolphin and reopen it, go to the same folder
7.  CPU usage should go up to 100% for one core, wait for it to calm down
8. Reactivate the preview in the settings, rego to the folder
9. CPU usage should be normal

EXPECTED RESULT
Preview should not be generated when previews are disabled. Also, it would be nice to have a little loading icon or at least a hint that something is computing when previews are generated...

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 43
KDE Plasma Version: 6.5.3
KDE Frameworks Version: 6.20.0
Qt Version: 6.10.1
Kernel Version: 6.17.8-300.fc43.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 12 × Intel® Core™ i7-10750H CPU @ 2.60GHz
Memory: 32 GiB of RAM (31.2 GiB usable)
Graphics Processor: NVIDIA GeForce RTX 2080 Super with Max-Q Design 

ADDITIONAL INFORMATION