I am trying to detect if a player is about to walk off the edge. This is how I've come so far:
 

    public void onTick(TickEvent.PlayerTickEvent event) {
        Minecraft game = Minecraft.getInstance();

        if (game.player == null) return;

        var playerBoundingBox = game.player.getBoundingBox();

        //double edgeDistance = 0.001;
        //var adjustedBox = playerBoundingBox.move(0, -0.5, 0).deflate(edgeDistance, 0, edgeDistance);
        var playerMotion = game.player.getMotionDirection();
        var adjustedBox = playerBoundingBox.move(playerMotion.getStepX(), playerMotion.getStepY(), playerMotion.getStepZ());

        boolean isColliding = playerBoundingBox.intersects(adjustedBox);

        if (isColliding) return;
        
        //doStuff();
    }

As you can see, I tried two approaches using boxes. One is commented out. Both of them do not work. Thanks in advance for any answers!

21 hours ago, author said:

Minecraft game = Minecraft.getInstance();

You should remove this to avoid reaching across logical sides. You can instead access the player via 'event.player'. As for your questions, I am not sure what you want to detect. But you can use the 'isOnGround()' method to check if an entity is currently on the ground or not.