SUMMARY

For testing I use a fresh Linux Mint installation. I have tried the official Ubuntu PPA, the official Flatpak and the Appimage.
All of them got the same issue, I cannot add a video file, which is located on a network share (in my case a samba share). If I use drag&drop the application does not show any response. The same thing happens if I try to add the file via right-click "add file/folder" - here kdenlive does not show the network shares if I click "Network" (Hint: In Linux Mint these shares are already mounted and fully accessible). Today I have tested the AppImage and in the console I get the following error messages:

I get this one, when I do drag&drop:
---
/////////// creatclipsfromlist (QUrl("smb://truenas.local/mediathek/Shows/TV/20210606 1820 - VOXup - Crossing Jordan    Pathologin mit Profil.ts")) true "-1"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
virtual QStringList Solid::Backends::UPower::UPowerManager::allDevices()  error:  "org.freedesktop.DBus.Error.Disconnected"
/////////// creatclipsfromlist return false
---

If I try to add the file via the "add file/folder" dialog and click network, I get this error:
---
/////////// starting to add bin clips
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
---

STEPS TO REPRODUCE
see description above.

OBSERVED RESULT
Nothing happens, no response (the Appimage shows errors in the console)

EXPECTED RESULT
To add the network share file like a local file

SOFTWARE/OS VERSIONS
Linux: Linux Mint 21.1 "Vera" Cinnamon 5.6.7 
Kernel: 5.15.0-56-generic