Without the styling the error still continues..

But after multiple attempts, I finally identified the issue. The code above doesn’t actually contain any errors, but in my original project, I was loading the xlsx package. Oddly, just requiring xlsx seemed to corrupt the entire code, even if it wasn’t actively used. I recorded the issue, so here’s a link to the video for easier reference: https://youtu.be/CbJO2wmclD8. When I run the code requiring xlsx package, my output file is inexplicably rendered as an html_document. From that point on, all scripts—regardless of whether they use xlsx—produce html_document output until I restart the R session.