It looks like the embedded [bootswatch themes ](https://github.com/quarto-dev/quarto-cli/tree/main/src/resources/formats/html/bootstrap/themes) currently use the v1 Google Fonts API that doesn't support variable fonts:

https://github.com/quarto-dev/quarto-cli/blob/a14f4b3090178f8e01f17e28a9e93d3f5b269065/src/resources/formats/html/bootstrap/themes/sketchy.scss#L169


It doesn't seem to impact behavior of themes now, but something to be aware of is the v2 Google Fonts API uses a different base URL, see:
https://developers.google.com/fonts/docs/css2
2021-04-22T23:33:06Z
apreshill
Future
open
v2 Google Fonts API?
https://github.com/quarto-dev/quarto-cli/issues/22