When you install a new app on Linux, the icon of the app will appear on the Applications Menu after installing it, but it won't appear on Desktop.
This is because on Linux, you need to create .desktop file manually to create a shortcut for the app that you want to be able to launch it from your Desktop.
Desktop shortcuts allow you to launch your app easily from your Desktop without having to browse through apps on Applications Menu, or using terminal.
Any text editor can be used to create a desktop file on Linux. However, the app that we'll be using for this tutorial, is an app that allows you to create desktop files easily by using GUI.
Instead of creating desktop files manually, you can do it with Desktop files creator
In this tutorial, you will learn how to install Desktop file creator, and how to create desktop files with it on Linux
Create Desktop files with Desktop files creator
To create a Desktop file by using the Desktop file creator app, is very easy.
First you need to launch Desktop file creator. You can do this by running the command below on your terminal
flatpak run com.github.alexkdeveloper.desktop-files-creator
Once Desktop file creator is launched, you can now use the app to create a desktop file on your system.
Begin by choosing a name for the app that you want to create the desktop file. For example, we are creating a desktop shortcut for Firefox, so the name of the app will be firefox

Next, you need to specify the executable path of the app
for example for firefox the executable path would be /usr/bin/firefox

Next, choose an icon. Simply click to the browse button and import the icon of the app

Next, set the category where you want the app to show up. If it's an internet app like in our case with firefox, then simply set "Internet" as the category. However, you can set any category you want.

Next, type a comment if you want. This field is not required so you can safely skip it.

The option "Not Displayed in Menu" allows you to choose whether you want the shortcut you are creating to appear on menu

Switch the "Run in Terminal" to ON only if the desktop file that you are creating is a terminal app, and you want it to be executed in a terminal window.

Once you are done with the configuration of your desktop file, you can now create the desktop file by clicking to "Create" button

Confirm that you want to create the desktop file, by clicking "OK"

And the desktop file will now be created on
.local/share/applications/file.desktop

Now that desktop file has been created, to make this desktop file appear on your Desktop, you need to copy the desktop file from /usr/share/applications/desktop.file
to your Desktop.
To do this, you can use the mv
command
sudo mv /usr/share/applications/desktop.file /Desktop
Now the desktop file should be showing on your Desktop

The reason why icon is showing with an X is because the desktop file by default it's not executable, meaning if you double-click it firefox won't launch.
To make this desktop file executable, right click over it, and then choose "Allow Launching"

And you should be able to launch the desktop file now

Install Desktop file creator
Desktop file creator can be installed on Linux by using flatpak.
To install Desktop file creator run the command below
flatpak install flathub com.github.alexkdeveloper.desktop-files-creator

Once you run the command above, you will get the following prompt on your terminal, simply press Y to confirm that you want to install Desktop file creator, then press enter.

Desktop file creator's installation process will begin after confirmation.
Conclusion
In this tutorial, you learned how to create desktop files with Desktop file creator. A flatpak app that allows you to create desktop files on Linux easily by using GUI.