For fun, here is a single table scan query that does the same
😎

USE TEEST;
GO
SET NOCOUNT ON;
-- https://www.sqlservercentral.com/Forums/1975311/Query-Help

;WITH...

Here is an example, should be enough to get you over this hurdle.
😎

Feel free to ping back if you need any further assistance.

[code...

Wrote a function for this a while back, you might find it helpful.
😎
Details in the comments.

USE TEEST;
GO
SET NOCOUNT ON;

GO