[FreeCAD 0.19] File export no longer works

Hello to FreeCAD and Linux users,

I have a problem to export files with FreeCAD 0.19: no file is saved when I do File -> Export... -> Save. No file is created in output, no matter which input or output format I choose.

I noticed that export window behaves differently. Graphically it is different and then the part name is not written automatically as usual (see attached file)

Yesterday I solved the problem by uninstalling FreeCAD and resetting Preferences but the problem reappeared today by, I think, simply because I reboot my system. Can anyone think of another solution ?

Thanks in advance for your answers,

OS: KDE Flatpak runtime (GNOME/gnome)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.14555 (Git shallow)
Build type: Release
Branch: (HEAD detached at 0.19.1)
Hash: a88db11e0a908f6e38f92bfc5187b13ebe470438
Python version: 3.8.8
Qt version: 5.15.2
Coin version: 4.0.0
OCC version: 7.3.0
Locale: French/France (fr_FR)