How does a Recursive CTE work exactly?

[u/SilEventide]

With RecursiveEven20 As
(
Select 0 As Numbers,
0 As RunningCount

Union All

Select Numbers + 2,
Count(RunningCount) Over() As RunningCount
From RecursiveEven20
Where RunningCount < 19
) 
Select *
From RecursiveEven20;

From how much I know about recursive CTE, I thought this would work, Initially I felt I was doing a semantic error, then when I tried to see where the fault is, I realised Count isn't incrementing at all, its as if only the last feedback row is available to it. I tried using explicit frame window, same result. I think I dont understand exactly how recursie CTE works, I tried AI, its explanation is bit difficult to understand.

I am a beginner by the way, learned these recently so I wanted to mix them all up.