This is a limitation of the default RMarkdown rendering engine. ggplot2 can access Windows system fonts just fine when you create a plot from the R terminal or R script, but it doesn't have access to them when you render a Quarto or RMarkdown chunk. You can fix it by changing the backend rendering engine to ragg. Install the ragg package with install.packages("ragg") and then add knitr::opts_chunk$set(dev = "ragg_png") at the top of your RMarkdown file to select ragg as your engine.