Problems and questions about sticky menus

I could find a solution for 1 and 2 by splitting the the submenu into 2 columns, here is the code if someone need it: ( i’m not an expert in css, played with some codes found on the internet )

I have no idea how it happened but the menu is sticky now on mobile…

.is-position-sticky ul.wp-block-navigation-submenu {
    display: grid !important;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
}

For problem 3, i solved it with CSS:

.wp-block-navigation-submenu {
    z-index: 999;
}