missing Plata-Noir in Budgie. An explanation for this?
Thank you in advance

Did you purposefully install it? On an existing installation, it won't simply jump into your installation by itself. Ie, I installed it yesterday after seeing it in a screenshot of a new install.

Thank you dbarron for your quick answer. How can I install it without doing a new install?

By selecting it in Software Center or by cmd line (eopkg install). If you're not up with eopkg search, then use the GUI.