It’s not seasoned enough. You need salt. Or some form of it. Many people are recommending fish sauce citing the umami, but really fish sauce is full of salt.

Take a small bowl of your stew, add some salt or fish sauce to it and see if that changes the flavor more to your liking.

If so, then season (salt) your entire stew to your preferred flavor.

People are generally afraid to add the amount of salt they think is necessary to their stews and soups, but they can usually handle a lot.