There are plenty of dialogs under Gtk3 which the OK/Cancle buttons are falling out of the screen area, due to the dialog too high/tall and can not be resizable.
This is a meta bug tracking all these dialogs.
This fault/bug is also on all my laptops using version 220.127.116.11 as at 25th April 2020 and has been present in all 6.4 versions.
As openSUSE Leap 15.1 uses their repository version, at present LibreOffice 18.104.22.168 and with XFCE all installed LibreOffice versions display this 'out of screen' dialogue error. There is no ability to resize for height of dialogue (width is resizeable). Can the smaller size with scroll bars to display full dialogue by scrolling be re-instated?