with the last Thunderbird update, the save menue is not a KDE menu anymore, it’s the Gnome menu. Firefox is using the correct KDE menu.
Some further info:
xdg-desktop-portal-kde6 is installed
in the settings "“widget.use-xdg-desktop-portal” is marked with “true”
Does somebody know, how to get back the KDE menus?
Firefox did not show the problem. I had a look in Firefox, here “widget.use-xdg-desktop-portal.file-picker” was on “1”.
I had a look on Thunderbird, the “widget.use-xdg-desktop-portal.file-picker” was on “2” and after changing it to “1”, Thunderbird is showing the KDE file menu .