This is still happening in the release version of 18.5. If you want to easily see the issue then run Apple's own Landmarks tutorial on iPad OS and compare how it looks on the 18.2 simulator compared to the 18.5 simulator. Here are screenshots of each...

Yes, I get this too. It's annoying on my desktop and extremely frustrating on my laptop. If there is no workaround at the moment can we at least be assured it will be fixed soon?

I am getting this bug as well in 18.4. Any NavigationSplitView in a TabView causes it. Setting the style to sidebarAdaptable does not help as when the tab selector is at the top the same issue occurs.