Well I had to try this in Excel and (after fighting the input format), it gave me

  2024-01-30 -> 2024-01-29
  2025-01-30 -> 2025-01-28

Fun. There is so much ambiguity in what “one month” means.

Polars has an offset-by function which is a bit more explicit about how you want to handle date math. “Calendar date” vs number of days.

Edit: just ran polars and I’m not in love with its answer either.