Add a sankey diagram option under the cash flow graph.

I think the UI/UX would be:

top: date range selection (date range, last year/month, last 30-60-90 days, this year, ytd, etc.) + filter and and search functionality you already have

middle: select date aggregation monthly, quarterly, or yearly to summarize income, expenses, and net (same as graph today). The graph should show ~15 bars of data, regardless of whether you pick month, quarterly, or yearly. Right now it randomly bounces around between 12 months of monthly, only YTD for quarterly, and 5 years for yearly. ~15 bars should fit nicely and allow to see trends. especially in year-over-year changes in monthly and quarterly spend.

bottom: toggle to chose between bar chart or sankey diagram. ENHANCEMENT: The bar chart/sankey should show all the data within the selected date range. only once a user selects one (or multiple) columns in the longitudinal date graph does it then filter down to that sub-date range). Right now it defaults to only being able to see one selected column of the longitudinal graph. So today, you can't say see all time spending for 10 years within the bar/sankey diagram.

if bar chart: summarization toggle to be category, group, or merchant (same as today).

if sankey diagram, would be great to see a toggle that allows for independent "layering" of category, group, merchant. i.e. you can select all 3 and the sankey would look like from left to right:

clicking into any of the layers of the sankey would then take you to transactions view, similar to what you've already built.

this way end users can be as granular as they'd like.