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