Very long start of dolphin

Describe the bug

I use package kdePackages.dolphin. When running dolphin from terminal, it starts very long (about 5-6 seconds to open window and about 5 seconds to render file tree), and icons doesn't render. But when I do

export QT_PLUGIN_PATH=/nix/store/x4ghagmp94ynzp5qdkdvia72g3i80awi-qtsvg-6.7.1/lib/qt-6/plugins:$QT_PLUGIN_PATH

it starts and works fine

Steps To Reproduce

Steps to reproduce the behavior:

Run dolphin from terminal
export QT_PLUGIN_PATH (see above)
Run again

Expected behavior

dolphin starts fine

Screenshots

Details

![image](https://github.com/NixOS/nixpkgs/assets/43654815/ea1d8d13-66e0-4ce6-9f8f-7e8b080a3a4a) ![image](https://github.com/NixOS/nixpkgs/assets/43654815/84d1f04c-8961-4cfd-8902-673e05471d27)

Additional context

I discovered what was missing by accident: I opened empty link from okular, and its opened fine, and then compared env from within dolphin (using embedded konsole)

Default $QT_PLUGIN_PATH:

/home/[user]/.nix-profile/lib/qt-5.15.12/plugins
/home/[user]/.nix-profile/lib/qt-6/plugins
/nix/profile/lib/qt-5.15.12/plugins
/nix/profile/lib/qt-6/plugins
/home/[user]/.local/state/nix/profile/lib/qt-5.15.12/plugins
/home/[user]/.local/state/nix/profile/lib/qt-6/plugins
/etc/profiles/per-user/[user]/lib/qt-5.15.12/plugins
/etc/profiles/per-user/[user]/lib/qt-6/plugins
/nix/var/nix/profiles/default/lib/qt-5.15.12/plugins
/nix/var/nix/profiles/default/lib/qt-6/plugins
/run/current-system/sw/lib/qt-5.15.12/plugins
/run/current-system/sw/lib/qt-6/plugins

What added when running dolphin:

/nix/store/8s65nma4p7w9g3xrg0dhcdaf30xqrwvl-dolphin-24.02.2/lib/qt-6/plugins
/nix/store/d643rzaa4ccgi6wi0rbvy6n85fb7dbmz-kio-extras-24.02.2/lib/qt-6/plugins
/nix/store/ijpkkfnwijdmz8ri58ps5kpyn5gja8vq-sonnet-6.2.0/lib/qt-6/plugins
/nix/store/4r8chci91if4dy7b1z0aa0idzc4sd8mx-baloo-widgets-24.02.2/lib/qt-6/plugins
/nix/store/pfl409khj0vcpnsdjgv9vvlj7y3kjrks-baloo-6.2.0/lib/qt-6/plugins
/nix/store/mk2vwkbg1k0lk4pnjyf1ri3cv8fzpkgy-kio-6.2.0/lib/qt-6/plugins
/nix/store/v3jhz3qyikdphx8hpwx4g7fnsr6k8174-kiconthemes-6.2.0/lib/qt-6/plugins
/nix/store/5d4k2b9lkcpdvdxb8zcwwcs5wmzf54vd-kauth-6.2.0/lib/qt-6/plugins
/nix/store/p4wvcpm0sh6mp19lii0qww95l3i18dba-kwindowsystem-6.2.0/lib/qt-6/plugins
/nix/store/8brf5yhjrq975masmiv808nwpjf1f41d-kidletime-6.2.0/lib/qt-6/plugins
/nix/store/hm64nn6i0h9j8acqfscys88ds72i5232-kfilemetadata-6.2.0/lib/qt-6/plugins
/nix/store/s2bsay385g0q1vy2a1jvv3w8g4g3pfkn-ki18n-6.2.0/lib/qt-6/plugins
/nix/store/rj6xqgzyjzw9xqa2jbv9k3wh84h25nmq-qtdeclarative-6.7.1/lib/qt-6/plugins
/nix/store/ikqvl8jq0d7vlp25d9zlbh44m4hljahc-qtbase-6.7.1/lib/qt-6/plugins

Dolphin version: 24.05.1 - from unstable. With dolphin from stable (24.02.2) behavior is the same

I also use qt5ct + kvantum

Notify maintainers

@K900

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.6.33, NixOS, 24.05 (Uakari), 24.05.1503.752c634c09ce`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.18.2`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

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