Drag and drop into Gajim Flatpak does not work (on Plasma Wayland) due to wrong mimetype

this

https://dev.gajim.org/gajim/gajim/-/blob/66f6ed7ff47e7121f5d25a1f2b9717b922f2400c/gajim/gtk/file_transfer_selector.py#L84

is not the correct mimetype

https://github.com/flatpak/xdg-desktop-portal/blob/a74c2ee93befca1f8583e86e165dbe90a0e72a15/data/org.freedesktop.portal.FileTransfer.xml#L30

it works on gnome because gtk originally had the wrong mimetype and still provides the wrong one for a couple releases for compatibility.

by Harald Sitter from upstream bug report https://bugs.kde.org/show_bug.cgi?id=490653#c4