kio-extras is part of the default install in KaOS, so not the issue.
Does the device register at all with dmesg?
dmesg | grep doro
And on a working distro, can you check what packages with mtp
in their name/description you have installed (something like mtp-server, mtpfs and so on).
Since the notifier recognizes the phone, did you try to set the phone to something like mediaplayer
in its menu?
And one more edit 🙂
Looks like this might be an issue with usb_modeswitch. As a test disable the switching (looks like usb_modeswitch is switching your phone to being a modem, not a USB storage device). Edit one file:
kdesu kate /etc/usb_modeswitch.conf
and set this line:
DisableSwitching=0
to:
DisableSwitching=1
This will need a reboot to take effect, so can only be tried on installed system. If this works, then revert the above (you don't want to globally disable usb_mdesiwtch forever) and a udev rule will need to be added.
If all this works for you, then this will become part of the default settings for KaOS, so I hope you don't mind trying this.