One option would be to add a ‘Navigation Menu’ widget to the ‘Top Bar’ widget area.
This would display a secondary menu in the top bar above the logo/site title/main menu area.
If you want the top bar menu to display below the logo/main menu area, add this custom CSS to ‘Customize’ > ‘Additional CSS’:
#masthead {
display: flex;
flex-direction: column-reverse;
}