Shapefile not displaying correctly

I’m very new to QGIS, but have used Arc a bit. I’ve downloaded a shapefile of the Home Owners’ Loan Corporation "residential security maps" from the 20th century (i.e. redlining maps). I collected the shapefile from the University of Richmond: https://dsl.richmond.edu/panorama/redlining/#loc=5/39.1/-94.58&text=downloads

In the QGIS browser pane I followed the filepath to the shapefile and dragged the holc_ad_data.shp onto the map pane. It will only show up as a single symbol (under "Layer Styling"). I want to show it (the layer’s "HOLC_grade" field) as categorized or graduated symbols with the actual HOLC colors (red, yellow, blue, green), but whenever I change it away from a single symbol it disappears in the map pane.

Could anyone clue me in on how I can set the layer to the "HOLC_grade" field and change it from the "single symbol" style without having it disappear? I would also like to be able to have my mouse click on the polygons and bring up their attributes, instead of only being able to pan with the mouse.