Latest update.
I have gone back to sorting out the original Eclipse problem (above).
Eclipse now works fine.
So what was the solution?
I first reinstalled Eclipse IDE
Eclipse IDE for PHP Developers (includes Incubating components)
Version: 2023-06 (4.28.0)
Build id: 20230608-1333
OS: Windows 11, v.10.0, x86_64 / win32
Java vendor: Eclipse Adoptium
Java runtime version: 17.0.7+7
Java version: 17.0.7
In my case I set up a workspace C:\eclipse-workspace and put my PHP project subfolders in that folder.
I then opened the projects in Eclipse from that folder. They opened up for editting ok.
When I tried to run them using the built in PHP server a browser session launched. This fixes the original
problem of it opening a Notepad session. So that;s progress.
But the problem was that it was looking to the c:\inetpub\wwwroot folder for project folders rather
than referencing the actual physical path for the projects,
I have been unable to find a way of changing that default in the system.
So I have moved all of my PHP project folders from the c:\eclipse-workspace folder to the
c:\inetpub\wwwroot folder and they launch as they shou;ld in the browser. Even without setting up any
specific sites for the project in IIS. I find it odd that Eclipse should default to what is effectively the default
folder for IIS on Windows systems.
Anyway it's now working now.
It would be nice to have some answers regarding these behaviours
but I will leave it there.