Variance within a Pivot Table

Hello - I am trying to figure out how in Excel to add in a column with a variance in the pivot table.
So in the image attached (I can't attach the raw data as PII and confidential customer information).

You will see I have a year column, then the rev by month as rows.
Trying to show...
- Year $$ by month (which it does)
- But the variance by % as well as an additional column!
So to say hey jan 2023 to jan 2024 had less (or more) sales in this category and the % difference is this? How do I add a 2nd column in this pivot to do that?
2nd image is my pivot details too.

I tried just to add a manual column but it's not copying down.

HELP
Thanks!

Attached sample excel

Attached is sample excel