Texts for creating better visualizations/presentations?

I started working for an HR team and have been tasked with creating visualizations, both in PowerPoint (I’ve been using Seaborn and Matplotlib for visualizations) and PowerBI Dashboards. I’ve been having a lot of fun creating visualizations, but I’m looking for a few texts or maybe courses/videos about design. Anything you would recommend?

I have this conflicting issue with either showing too little or too much. Should I have appendices or not?