It’s a common mistake you could have.
If you have this overlay on header, you need to setup some settings.
See header on this page. it’s overlap.
The header type should be “Default menu” not “Transparency menu on this page”.
If you see your theme settings, the default type is “Transparency menu”
If the navi type is “Default as theme settings”, it means it follows global setting from theme settings.
It also means, it’s “transparency”.
Then you need to change it to “Default menu”.
Like this. then it will solve this issue.