Show guide line between tiled windows on hover
Most systems supporting basic tiled-based navigation distinguish normal window layouts from tiled ones by putting some sort of separator line between them, either always (macOS) or on hover (Windows 10). This is very useful not only because it intuitively indicates that the two windows are tiled, but also makes re-arranging the space between them easier thanks to the larger clickable area whenever (frequently) needed.
As an alternative, sometimes windows are separated by a narrow transparent space between them (showing the background/windows below, see Windows 10 with "arrange windows as tiles" option), but I personally tend to find that much more distracting and uncomfortable.