Hello,
1/ Custom header is used on the demo for the Home page https://xstore.8theme.com/elementor/demos/ecoenergy/ , header overlap is activated also. Here is a video about Multiple headers – https://youtu.be/BpeXfzNwkOc
2/ Theme Options > Header builder > delete elements from the connection block and disable separator https://prnt.sc/224uhg8
Regards