There are a lot of healthy fermented foods you can include in your diet. Pickles, sauerkraut, kimchi, kombucha, yogurt, skyr, kefir, etc. Miso and doenjang are similar and they’re great to use in your cooking but I can’t imagine just drinking them for the sake of it. I believe deonjang is kinda chunky so mixing it with water would be kinda gross. You could use it to make a nice soup or stew like jjigae, then you’re getting some extra micronutrients from the veggies too.