There seems to be an issue on at least Safari 14 and up on various macOS versions where the subgroup breadcrumb navigation drop-down no longer renders correctly. Hovering it shows the tooltip and clicking it starts to show the navigation drop-down, but something seems wrong with the CSS causing it to be mostly hidden behind other elements and not clickable.
You can see the tooltip showing (the mouse cursor is hovering the 3-dots navigation element), clicking it shows the top of the drop-down getting rendered underneath everything below it, and a scrollbar appears on the right side. Seems to be a z-index and overflow thing? This is on gitlab.com.