On the world map, there are 6 zones you can travel to, but only 5 buttons displayed across the top. If you want to get to Chult, you have to use the arrows on the side. Worse, when you click the arrows the buttons move, meaning the zone you're looking for is no longer in the same place as it was a second ago. Buttons should not move around the UI: PE is always on the same place when you load the map, so the button to see the Chult map should ALSO always be in the same place.
A better design would be to show all 6 at once - there's tons of room. And for future expansions that add zones, shrink the bar on top or run them down the side, or re-use "global" maps like Storm King's Thunder does with the IWD map.
Second suggestion: Have the world map open to your current zone's world map, to make it easier to travel between Chult zones or between IWD zones or between Undermountain zones if you're in them. If I'm in any of those submaps with multiple locations and I want to fast travel, I want to STAY IN the sublocation far more often than I want to leave it, so that should be the default.
Third suggestion: Some of the map choices are kinda pointless. Underdark only has one location, for example, unless you have a specific quest. You should add The Yawning Portal to the main map, and clicking it would take you to the Undermountain map, and add another button for Undermountain to the Underdark map. It's still two clicks away like now, but now you've got a second item on the Underdark map, you've eliminated a top-level map meaning you can show all 5 at once even with the current interface.