Rank stacked column chart

You could use RANKX to create a calculated column that ranks each category. You just have to make sure that each category only has 1 rank, so every year for that category and every month it must be the same number ranking. 



Then you can use Sort By Columns to sort the category by rank and the legend will automatically update.

https://docs.microsoft.com/en-us/power-bi/create-reports/desktop-sort-by-column


You may also be interested in Ribbon chart, which shows relative rank for each category and how it has changed from month to month: https://docs.microsoft.com/en-us/power-bi/visuals/desktop-ribbon-charts