Description:
**Bug Details**
When using the Flathub flatpak of LibreOffice on Fedora Kinoite and SteamDeck's SteamOS, the Open/Save-As Dialog boxes do not conform to the system. This prevent LibreOffice from accessing bookmarked locations and remote servers (through the Plasma I/O stack). LibreOffice's flatpak is the primary means of LibreOffice on SteamOS and possibly future Fedora releases (see 2023 RHEL changes). Conforming to xdg-portals (files selection) for just the flatpak would be helpful for this emerging platform.   





Steps to Reproduce:
1.Install LibreOffice via Flathub on SteamOS or Fedora Kinoite
2.Open blank document and select Save As
3.Observe the GTK file picker instead of the xdg-portal default (KDE file picker) 

Actual Results:
Regardless of Linux platform, the GTK file picker always appears.

Expected Results:
LibreOffice's flatpak would give deference to the host system for the Open and Save-As file picker. 


Reproducible: Always


User Profile Reset: No

Additional Info:
**LibreOffice Details**
Version: 7.5.4.2 (X86_64) / LibreOffice Community
Build ID: 36ccfdc35048b057fd9854c757a8b67ec53977b6
CPU threads: 4; OS: Linux 6.3; UI render: default; VCL: gtk3
Locale: en-US (en_US.UTF-8); UI: en-US
Flatpak
Calc: threaded

**System Details**
Operating System: Fedora Linux 38
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.107.0
Qt Version: 5.15.9
Kernel Version: 6.3.7-200.fc38.x86_64 (64-bit)
Graphics Platform: Wayland
Graphics Processor: AMD Radeon RX 480 Graphics