Recently, I found that there are two org.gnome.Software.desktop files in two places:
one in

/usr/share/ubuntu/applications/

and one in

/usr/share/applications/

Can someone explain why (and how)

/usr/share/ubuntu/applications/org.gnome.Software.desktop

is loaded on the left rather than the latter?

Content of the file /usr/share/ubuntu/applications/org.gnome.Software.desktop

[Desktop Entry]

Name=Ubuntu Software

Comment=Add, remove or update software on this computer

# Translators: Do NOT translate or transliterate this text (this is an icon file name)!

Icon=ubuntusoftware

Exec=gnome-software %U

Terminal=false

Type=Application

Categories=GNOME;GTK;System;PackageManager;

# Translators: Search terms to find this application. Do NOT translate or localize the semicolons! The list MUST also end with a semicolon!

Keywords=Updates;Upgrade;Sources;Repositories;Preferences;Install;Uninstall;Program;Software;App;Store;

StartupNotify=true

MimeType=x-scheme-handler/appstream;x-scheme-handler/apt;x-scheme-handler/snap;

X-GNOME-Bugzilla-Bugzilla=GNOME

X-GNOME-Bugzilla-Product=gnome-software

X-GNOME-Bugzilla-Component=gnome-software

X-GNOME-UsesNotifications=true

DBusActivatable=true

X-Ubuntu-Gettext-Domain=gnome-software

Here is my desktop screenshot (Notice the left dock)

Here is my Ubuntu version:

$ lsb_release -a

No LSB modules are available.

Distributor ID: Ubuntu

Description:    Ubuntu 18.04.5 LTS

Release:    18.04

Codename:   bionic

I found that I can get the list of my apps from this command:

$ gsettings get org.gnome.shell favorite-apps

['firefox.desktop', 'thunderbird.desktop', 'org.gnome.Nautilus.desktop', 'rhythmbox.desktop', 'libreoffice-writer.desktop', 'org.gnome.Software.desktop', 'yelp.desktop', 'org.gnome.Terminal.desktop', 'gnome-control-center.desktop']

Therefore, I think my question can reduce to: Is there an environment variable determining which org.gnome.Software.desktop is loaded?