Can't render a qmd presentation

Hi all,
I have a qmd/revealjs presentation, but I have customised the theme and have created a template. The slides compile perfectly, but when I try to pdf them using renderthis I get a message

Error in to_pdf_complex(path_from(step_html, "url"), output_file, partial_slides,  : 
  Input does not appear to be xaringan or quarto slides:

I think this gets triggered by the check in

has_remark <- b$Runtime$evaluate("typeof slideshow !== 'undefined'")$result$value
  if (!has_remark) {
    stop("Input does not appear to be xaringan or quarto slides: ", input)
  }

Not sure how to deal with this though...

I'm testing this on a html file output by quarto both locally and deployed online (https://giabaio.github.io/test-quarto). Sorry if I'm missing an obvious point!

Thanks for your help!
Gianluca

Reproduce the failure with the linked Quarto-generated HTML and inspect the renderthis path that evaluates typeof slideshow !== 'undefined'. Determine how the qmd/revealjs output differs from the supported slide formats; done means the linked presentation can be rendered to PDF without the input-format error.