If the flavor is too bitter, the Dalgona candy is burnt. Some tips to ensure non-burnt Dalgona:
Add baking soda when the caramel is light yellow. The caramel will continue to darken and cook throughout the rest of the cooking process so don’t wait until the caramel is brown.
Remove the saucepan from the heat source immediately! I transfer to a quartz countertop to further prevent burning the caramel.
Use a heavy-bottomed saucepan. The thick bottom will help to moderate the heat and prevent the caramel from turning dark too quickly.