Isn’t that an overall kwantum theme? In either case, the window decoration is probably an aurorae theme. Install it manually in ~/.local/share/aurorae/themes.
EDIT: I checked. It’s a kvantum theme with aurorae window decoration. So, the theme should be in ~/.config/Kvantum/. Provided you have kvantum installed of course. The application style needs to be set to kvantum. The theme has to be set in the kvantum manager and the window decoration to utterly.
Thanks, my friend—you’re right. Yesterday I did a bit more digging, and the description says the global theme only includes part of the configuration, and the rest has to be done manually. I’m new to this, so it feels a bit confusing, but it seems you have to download the .tar.gz files from the official site. There I saw instructions mentioning that part of it should be set up with Kvantum, and the other configurations go into different folders.
I’ve looked for videos, but they don’t really match this specific case. Maybe you could share a tutorial or some material that helps explain how to apply a theme manually?