Submenu missing link separators

I have several Websites on air with the Sydney theme. In a new project with version 6.0.2 the submenu-items are, on non-mobile screens, no longer separated by a separator line. And because the line spacing within the submenu items (in case it is a longer text) is quite similar to the line spacing between the submenu-items, this can be confusing for end-users. So I am looking for a css code that I can put in the additional css, to add line separators between the submenu items.

By the way: for the mobile header it should be possible to opt for line separators (called “link-separators) in the customizer>mobile header>style>offcanvas-menu section. For now this doesn′t work neither. But I guess this should be another topic. However this additional info might be helpfull for analysing and finding a solution for this topic.

I already changed the colors of the diffrent elements to exclude the possibility that the problem is due to overlapping or same colors for the backgounde color and the separator line color. This was/is not the case and brought no solution.

Thanks ahead for your help!

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