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SUMMARY


STEPS TO REPRODUCE
1. 
2. 
3. 

OBSERVED RESULT


EXPECTED RESULT


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION


Thanks for your understanding

STEPS TO REPRODUCE:
1. Open Dolphin
2. Can browse MTP mounts
3. Open Dolphin's File picker
4. MTP mounts are not displayed

OBSERVED RESULT
MTP mounts are not displayed

EXPECTED RESULT
MTP mounts should appear and be browseable just like it happens in Dolphin

SOFTWARE/OS VERSIONS
Linux NixOS 25.05
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.0

ADDITIONAL INFORMATION
I installed the following related packages:
android-tools
go-mtpfs
kio-fuse
kio-extras
android-udev-rules
mtpfs
libmtp
jmtpfs

Thanks for the additional information. I tested this here and can't reproduce the problem with git-master
When I have my Android phone connected, I can see it under Devices both in Dolphin and with File - Open in Firefox (using the KDE file dialog). 

Can you provide more detail about what application you're invoking the file picker from?
What kind of mtp device do you have connected?
A screenshot of the application and file picker window would be really helpful. Thanks.

> Can you provide more detail about what application you're invoking the file picker from?
Any. I just tried Firefox, as you mentioned it, "Save Page As...", the MTP mount is not there, I can see it in Dolphin though,

> What kind of mtp device do you have connected?
Any Android Phone

> A screenshot of the application and file picker window would be really helpful.
The MTP device simply doesn't appear on the left, as if it was not connected. I found it's a pretty common bug  in KDE, it has been going on for several years, but I couldn't find anyone who reported it upstream.

Please attach a screenshot so we can make sure that you're not actually encountering a limitation of the GNOME file dialog.

Also, please test with a KDE native app like KWrite or Kate.
Please attach a screenshot of the File - Open dialog from one of those, while your phone is attached.

Thanks.

You are right guys, I never noticed, but with native KDE apps it works correctly, with all other apps, even Qt ones, it doesn't. How do I fix it?

I had a feeling. Here are your options:
- Switch to KDE Plasma as your DE so that plasma-integration is running, which at least makes Qt-based apps use the KDE dialog
-- If you're already using Plasma, then your system is apparently semi-broken, perhaps due to you using qt5ct or qt6ct
- Switch to better apps that use the KDE file dialog
- Try to force the app to use the KDE dialog dialog via the xdg-desktop-portal (note that with Firefox this carries elevated risk of crashes)
- Ask the app developer to change the code to deliberately switch to the KDE file dialog when run in Plasma, or use the portal so this happens automatically
- Be sad

> - Switch to KDE Plasma as your DE so that plasma-integration is running, which at least makes Qt-based apps use the KDE dialog
KDE is the only DE installed, I didn't have plasma-integration installed, but installing it dodn't fix the issue.
> -- If you're already using Plasma, then your system is apparently semi-broken, perhaps due to you using qt5ct or qt6ct
There are no Qt5 dependencies to my knowledge
> - Switch to better apps that use the KDE file dialog
Only native KDE seem to work, I don't know if it's just bad design from other devs
> - Try to force the app to use the KDE dialog dialog via the xdg-desktop-portal (note that with Firefox this carries elevated risk of crashes)
How do I do this?
> - Be sad
Already am :(

If you're using Plasma but you didn't have plasma-integration installed, then your system was very much misconfigured. I'd recommend you ask for help in getting your system into a better state from the packagers or power users of your chosen distribution.

https://community.kde.org/Distributions/Packaging_Recommendations may also be helpful.

NixOS is a minimal distribution, users are supposed to install additional features themselves. That link is useful, thank you. Is there something more related to my issue? I could find nothing, just that many other people experience the same issue on different distributions. I asked in my distro's forums, but apparently nobody knows how to change the file picker globally.
I also installed these other packages since then, because someone somehow fixed it with some of these, but nothing worked
    plasma-integration
    xdg-desktop-portal
    xdg-desktop-portal-gtk
    xdg-desktop-portal-kde
    gsettings-qt
    gsettings-desktop-schemas
    gnome-settings-daemon
    plasma-browser-integration

Minimal distributions are basically tools for hobbyist or professional OS builders. If you use one, you become an OS builder, so it's your responsibility to ensure the system ends up in the state you want it.

Basically you need plasma-integration installed, and then you also need to make sure you or any other non-KDE package aren't setting or overriding the QT_QPA_PLATFORMTHEME or QT_STYLE_OVERRIDE environment variables.

There are so many combinations possible that it's doubtful I can help you further than that.

I never had such issues with other desktop environments, this is the first time something like this happens, and I can't see why the GTK file picker should be opened in place of the KDE file picker. I installed everything and even more, and followed what I found in other related threads. Many people has this exact issue even on bigger distributions such as Ubuntu or Fedora.

Thank you for your help, I hope the KDE team will find a fix for everyone.