It works, thanks.
But there is no way to control which menu item (there can be more than one) should be on the right (my code below works too, but lacks understanding of how the new theme works).
Well, this is not in the documentation, which is very bad (with the transition to the new version of the GP, a lot has changed)
@media(min-width: 1024px) {
.main-navigation .inside-navigation .main-nav {
flex: 1;
}
/*.main-navigation li:last-child {
margin-left: auto;
}*/
li.menu-right {
margin-left: auto;
}
}