Mobile Menu

You can:

1. Add this CSS:

.line-above {
    position: relative;
}
.line-above > a:before {
    content: '';
    position: absolute;
    top: 0;
    left: 20px; 
    right: 20px;
    border-top: 1px solid;
}

2. Edit your Menu, and any item you want a line above add a CSS class of line-above to it.
See here how to add CSS class to menu item:

https://docs.generatepress.com/article/using-the-wordpress-menu-builder/#custom-classes

Wonderful! Thanks a lot! It's done and I learned a lot.
Great help! Thanks

Glad to hear that