Place almond milk and apple cider vinegar in a small bowl. Stir and set aside.
Place bananas in a large mixing bowl. Use a potato masher or fork to mash them well. Add maple syrup, oil, and vanilla, stirring to combine. Stir in almond milk.
Add flour, baking soda, salt, and cinnamon. Stir just until just barely combined (a few flour clumps are okay). Gently fold in in blueberries, being careful not to over-mix.
Fill muffins three-quarters full. Bake for 25 minutes, or until a toothpick comes out clean. Cool muffins on a wire rack for 15 minutes before removing from tin to cool completely. Store in an air-tight container at room temperature for a couple days, refrigerate, or freeze for later.