You need to stretch the ul so it takes up the available width and then you can just use a margin-right auto on the logo to push the other items all the way over to the right.
nav {
display: flex;
/*justify-content: end;*/
}
nav .menu{flex:1 0 0;align-items:center;}
nav .menu .logo{ margin-right:auto;}
I’ve mentioned this before but you cannot have a div as a direct child of a ul!! Only list items can be direct children so change the div to a list item.