Feed the sourdough starter and allow it to become active and bubbly at room temperature, confirming readiness with the float test. In a stand mixer bowl, combine the starter, filtered water, and coconut sugar, stirring with a wooden spoon until mostly blended. Affix the bowl to the mixer with the dough hook, incorporate 2 cups of flour on low speed, then gradually add the remaining flour while mixing slowly. Let the dough rest for 15 minutes. Add the salt, then mix for a few minutes until thoroughly integrated and the dough forms a cohesive ball. Transfer the dough to a greased glass or ceramic bowl, cover with plastic wrap or a damp tea towel, and leave to ferment at room temperature for approximately 10 hours. Near the end of fermentation, line a baking sheet with parchment paper. Turn the dough out onto a lightly oiled surface and divide it into 8 portions. Shape each portion by gathering the edges, pinching them into the center, then turning the seam-side down to create a smooth ball, enhancing gluten structure. Poke a hole in the center of each ball with your thumb and gently rotate to widen the hole, remembering that it will contract during the second rise. Arrange the bagels on the prepared baking sheet, cover with a tea towel, and let rise for about an hour until noticeably puffed. Meanwhile, bring a large pot of water to a boil and preheat the oven to 425°F. Once the water is boiling, stir in the baking soda and coconut sugar. Using a slotted spatula, gently lower each bagel into the boiling water, boiling only 3 at a time for 1–2 minutes per side. Return each boiled bagel to the parchment-lined sheet and immediately sprinkle generously with zaatar while still damp. Repeat until all bagels are boiled and seasoned. Bake for approximately 25 minutes until golden brown. Allow the bagels to cool slightly before serving with your spread of choice.