Header V3 is a pre-configured header layout of Konte. In order to select it, just go to Customize > Header > Header Layout and select Prebuilt Header as Header V3. With all header layouts, you can select header background, text color, set the height in the Customizer. Besides, the Topbar can be configured separately.
This header layout supports only the Header Main section. You can set the header main‘ height and background in Customize > Header > Header Main.