I've only run this editor acouple of times after installing and now every time I run it I get a message saying:

"Can't access Esenthel Server, check your firewall"

Is it not possible to run the editor without being online, updating and allowing a server
to run on pc ??

This message shows only when you want to install The Editor and you can't connect to Esenthel Website to download the files.

I installed the editor but when I blocked the Titan Server through firewall I got that message. I also moved the install to another drive when I first got the message.
Only wondered why the editor needs to be run and access the net ?

The Fantasy Demo is awesome BTW, which is why I was curious about the engine.
Would like to try it out more but the editor does not compile or run my projects with my VS2017. Does the source code include the source for editor so I can compile the editor also ??

Yes there's source included for Editor as well.
But I can't confirm it will be easy to make it work on VS 2017.
I had multiple versions of VS installed at the same time, and never had a problem.
So you can try to have VS2017 and 2026 side by side.