Question LTS Ubuntu with Unity and Visual Studio Code

Just installed LTS Ubuntu on my machine and installed Unity with the Unity Hub.
After that I installed Visual Studio Code with the following extensions:

Set the Editor to Visual Studio Code in Unity, and all seems good....
Also installed the .net SDK
All works, but the intellisense for Unity specific API things like .transform, OnEnable(), and that stuff is not showing up.
Pls help me. How can I get the intellisense to work for Unity API related stuff?
thanks

 

thanks for the response. The link you gave me was actually the one post I followed to get it to work somewhat.
When I open up a .cs file in Visual Studio Code I get this error:



Not to sure about this output.
However the post does mention that I need something called OmniSharp... :
"2. Open VS Code and install de C# extension OmniSharp (you will be asked to install it when you open VS Code). After tah close VS Code"

Again this extension does not show up under extensions so I cant install it:


However under settings I found this:


But even after switching on OmniSharp nothing changes.
Thanks for reading and any help welcome.

 

I think I know what the problem is....
It seems Mono is not installed correctly.
But if I follow this:
https://www.mono-project.com/download/stable/#download-lin
I keep getting errors.
I tried this:
https://www.mono-project.com/docs/getting-started/mono-basics/
just to see if Mono works.
However I cant even compile my file with:
csc hello.cs
or
mcs hello.cs

meaning there is something wrong with Mono

Edit:
I followed this:
https://linuxize.com/post/how-to-install-mono-on-ubuntu-20-04/?utm_content=cmp-true

and now Mono is correctly installed and working.