This "minimal working example" uses PlantUML and GraphViz via Pandoc's official diagram-generator filter so you must install them and configure your system's environment variables according to the filter's documentation. Note that the filter is included in this repo for simplicity.
Quarto commands of interest:
To generate a PDF version (note the pdf-engine: latexmk setting in _quarto.yml):
quarto render diagram-test.qmd --to pdf
To generate the HTML version (note the self-contained: true setting in _quarto.yml):
quarto render diagram-test.qmd --to html
Some have had trouble using SVG images because LaTeX doesn't support it natively.
I have found that pdf-engine: latexmk allows it to work with no other configuring.
Perhaps this example will be of use to you.
quarto render svg-test.qmd --to pdf