This blog was created using Jekyll with Minima theme via Ruby Gem. While the Minima theme has been receiving continuous updates, the version in github-pages plugins was still on 2.5.1, which was created back on 2019-08-16. There is a pull request to create a new release tag. However, until that happens, you can use jekyll-remote-theme to access the latest version directly, as suggested by ashmaroli.

# _config.yml

# Add to plugins: list
plugins:
  - jekyll-remote-theme

# set up remote_theme
remote_theme: jekyll/minima