That is because the HUD is selected based off the game mode. You either need to edit the existing game mode to use your HUD or create a new game mode that uses your HUD and set it as the active game mode in the world settings.
I created a blueprint HUD class so that I can display variables, but I’m having trouble selecting the new HUD. I went to world settings, but the ability to select the HUD Class is grayed out.
Ah ok, I was able to add it to the game mode through the c++ code.
i also have the same problem ,can you tell me how to edit it in the c++ code?
I think this happens if your game mode class is a C++ implementation. In any case you can in your constructor or BeginPlay() of your Game Mode class do:
HUDClass = YourCustomHUDClass::StaticClass();
This should assign the HUD to your gamemode
Found a possible workaround by adding a component, and then dragging the correct one on top of the default one.