The first and the third items are both the Chromium browser. The former is a snap package and the latter is a Debian package.
You can confirm this from the version numbers and descriptions. The first:
matches:
$ snap search chromium
Name Version Developer Notes Summary
chromium 62.0.3202.75 canonical - Chromium web browser, open-source version of Chrome
The second:
matches:
$ apt search chromium-browser
Sorting... Done
Full Text Search... Done
chromium-browser/xenial-updates,xenial-security 62.0.3202.75-0ubuntu0.16.04.1313 amd64
Chromium web browser, open-source version of Chrome
and the AppStream description:
$ appstreamcli search chromium
Identifier: chromium-browser.desktop [desktop-application]
Name: Chromium Web Browser
Summary: Access the Internet
Package: chromium-browser
Icon: chromium-browser_chromium-browser.png
Using the gnome-software
command should help. Both of these commands open the third entry:
gnome-software --details=chromium-browser.desktop
gnome-software --details-pkg=chromium-browser
Here, chromium-browser.desktop
is the AppStream ID, and chromium-browser
is the package name.
Best Answer
They are hidden because they are marked as technical packages - the ones with no .desktop file (see How does Software Center determine what is a "technical item" and what isn't? ).
You can use Show # technical items link in the bottom left corner to see them.