These are the theme files that were bundled with Cinnamon 6.2.9. To use this as a theme for Cinnamon, simply install the cinnamon-6.2 folder to
/usr/share/themes
or
/home/username/.local/share/themes
If you are on Arch or an Arch-derivative, you can also download the package from releases, or install from the AUR here.
Then, you can apply the theme from within Cinnamon by opening up Themes from Settings.