Maybe this fits here as a mention: if the template uses metadata other than that defined by quarto, you have to also set `validate-yaml: false` or quarto will refuse to render the document.

https://github.com/quarto-dev/quarto-web/blob/89ed76a15ca8debeb1871d04499759a543da6a4b/docs/reference/formats/html.json#L515
2022-02-05T14:04:31Z
jmbuhr
closed
disable yaml validation for some custom pandoc templates
https://github.com/quarto-dev/quarto-cli/issues/312