In a large saucepan, melt the butter over medium heat. Add the onion and cook until softened, 2 to 3 minutes. Stir in the strawberries, port, sugar, lemon juice and thyme and cook until the strawberries begin to soften, 2 to 3 minutes. Add the raspberries and blueberries and cook until the blueberries swell and the compote thickens slightly, 2 to 3 minutes. Stir in the ginger, if using. Serve warm or at room temperature.