Linux GUI

What about

sudo systemctl isolate graphical

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Some resources on that topic:
https://linuxconfig.org/start-gui-from-command-line-on-ubuntu-20-04-focal-fossa

https://linuxconfig.org/ubuntu-20-04-gui-installation

You asked, "How exactly do I get the desktop environment to show from the initial terminal window?"

1) You must have access to a graphical display.

2) Per #1, this might be a physical display or a pseudo display where you run the remote machine over a tunnel, which will require you having software available locally which can accomplish this action.

3) You must ensure some sort of graphical software is installed on your remote machine, if machine is remote.

Best to answer the following.

1) Is this machine remote or local, where local means you have access to a physical keyboard/mouse/display.

2) What Linux Distro + Distro version is running.

3) Did you install this Linux instance or someone else.

Alex
What exactly does your command do

Taken from https://linuxhint.com/systemd_hot_it_starts_your_system/

Setting the “runlevel”, called a target.

You can change the target while running, for example you could use a terminal to set your target to multi-user. This would stop your GUI, X or Wayland but let you and others, log in with a text console. Use the following command.

$ systemctl isolate multiuser.target

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Or, if you want to start your desktop, use the following command instead.

$ systemctl isolate graphical.target

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What you are really interested in is how to start the correct level, you can find out what you have right now this way.

$ systemctl get-default

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To change the default set it.

$ systemctl set-default graphical.target

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This command actually makes a lot of units and services start as you boot your computer. You may want to start or stop a single service though.

Alex
I am not so familiar with linux
To start, all I want to do is to see the Desktop GUI?
What do I use as a command

Did you try 

sudo systemctl isolate graphical

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?!
Did you install Ubuntu yourself?
Where does it run?

I am using the WSL on windows

Thanks Alex

Thanks all
Sorry - I should have made it clear upfront that I was using WSL

No problem ;-) but, keep that in mind for the next time!