Warm the olive oil over low heat in a large saucepan or Dutch oven.
Add minced garlic and cook for one minute, stirring occasionally.
Put in the sliced mushrooms, dried thyme, onion powder, salt, and pepper and cook over medium heat. Cook until mushrooms have softened and reduced, stirring occasionally, for about 5 minutes.
Pour in the apple cider vinegar and stir mixture, followed by the vegetable broth and coconut milk.
Sprinkle the rice flour (don't pour) over the mixture and stir until dissolved. Bring to a boil and then reduce heat, cover, and simmer for 20 minutes.
Use an immersion blender and puree half of the soup. If you don't want any full mushroom slices remaining, blend soup until smooth. Don't have an immersion blender? Carefully blend hot soup in batches in a high speed blender, ensuring lid is secured.
Season with additional salt and pepper, if desired. Serve warm.