Thank you for the reply! And sorry, I should've made it more clear that I am working in RStudio Cloud (things work just fine in RStudio Desktop). The reprex is at the RStudio Cloud link in my post. Is that not the right way to to provide it?
I have been able to use showtext as a workaround, but unfortunately it is not quite enough for my use case. It works by computing the outline for the font and drawing that, but the result is that the final PDF does not actually include the text itself- it's just got the outlines for the glyphs, so it displays on the screen OK, but it is not possible to copy and paste the title, etc. out of the PDF. Ragg produces raster output, and I need vector output.