In Save dialog on Plasma 6.1.4 with Wayland the “Cancel” and “Save” buttons are positioned in the upper side of the window, the first in the left edge and the second in the right edge (see the screenshot below).
This arrangement is absolutely not ergonomic.
The buttons are in not natural positions and are difficult to find in the dialog. Moreover it requests big mouse movement to reach them.
That’s the save dialog GTK apps use, KDE is not responsible for it. Some of them can opt in to use KDE dialog but depends on the app. Also for Firefox you might need to toggle some flag in about:config.