To build, have hyprland headers installed and under the repo directory do:
make all
Then use hyprctl plugin load followed by the absolute path to the .so file to load, you could add this to your exec-once to load the plugin on startup
hyprpm add https://github.com/Moerliy/Hypr-Which-Key
hyprpm enable Hyprspace
Refer to the Hyprland wiki on plugins, but your flake might look like this: