Yes, indeed it seems
gnome-desktop-item-edit is removed from the
gnome-panel package, it won't be available for Ubuntu 19.10 (and most likely later releases).
As an workaround you can create
.desktop files by hand. Just create a blank text file and add the following lines to it for a simple one:
Name=<NAME OF THE APPLICATION>
Comment=<A SHORT DESCRIPTION>
Icon=<ICON NAME OR PATH TO ICON>
Then rename the file as
APPNAME.desktop and right-click and select 'allow launching' (you may also have to make it executable).
.desktop files for installed applications are usually found in your
/usr/share/applications/ directory (or
/var/lib/snapd/desktop/applications/ for snap applications). You can copy a
.desktop file from there.
For a GUI alternative you may use
alacarte (aka 'Main Menu'). Install it by running (the 'universe' repo needs to be enabled)
sudo apt install alacarte
It creates a
.desktop launcher in your
~/.local/share/applications/ directory by default (and hence it makes the application available in your list of applications, so that you can launch it from your Activities overview or Applications overview). You can copy the created
.desktop file afterwards.