This was reported in Installing Extensions in RStudio · quarto-dev/quarto-cli · Discussion #7851 · GitHub and solved in Installing Extensions in RStudio · quarto-dev/quarto-cli · Discussion #7851 · GitHub and also upstream at docs(readme): update owner and repo name by mcanouil · Pull Request #1 · coatless-quarto/illinois-revealjs · GitHub
So it should work fine now.