It's frustrating when articles like this don't mention the version of the software tested. Because that does matter.
From the PostgreSQL 14 release notes: "Allow hash lookup for IN clauses with many constants (James Coleman, David Rowley). Previously the code always sequentially scanned the list of values."
And in PostgreSQL 15: "Allow hash lookup for NOT IN clauses with many constants (David Rowley, James Coleman). Previously the code always sequentially scanned the list of values."
From the PostgreSQL 14 release notes: "Allow hash lookup for IN clauses with many constants (James Coleman, David Rowley). Previously the code always sequentially scanned the list of values."
And in PostgreSQL 15: "Allow hash lookup for NOT IN clauses with many constants (David Rowley, James Coleman). Previously the code always sequentially scanned the list of values."