Currently, DISTINCT is implemented by creating a GROUP BY with all the non-aggregate columns. This causes DISTINCT to be executed before Window Functions, and it includes the partition and order by columns from the window function. The standard is do the uniqueness after Window Functions, just before UNION (if any). The results are similar, unless Window Functions are involved, in which case, the DISTINCT being executed before Window Functions deletes rows that should be included in the Window Function processing, resulting in the wrong answer.

This page shows the expected order of SQL processing: https://www.eversql.com/sql-order-of-operations-sql-query-order-of-execution/