What am I doing wrong creating a Pie chart!?

I could not find a chart in your file, so I could not see what you are trying to do when you create a chart. I also could not find a summary table anywhere in the file where you summarize the data in either table. Your observation that you get "a ton of the same categories" further suggests that you are not summarizing the data anywhere. Remember that charts have essentially no computational or summarizing ability, so, when we want a chart to summarize data, we first need to summarize the data somewhere in the spreadsheet before creating the chart.

As a guess, I chose to create a pivot table. Select one of the raw data tables, insert a pivot table (not sure exactly how your version does that. this tutorial might help, if it applies to your version https://www.excel-easy.com/data-****...ot-tables.html ), instruct the pivot table to use "item category" as the row labels and "sum of inv. value" as the pivot table values. Then insert a pie chart based on the pivot table. If desired, you can filter the pivot table to show only categories you are interested in seeing.

Does that help?