In a small saucepan over medium heat, combine water, white sugar, and brown sugar.
Stir until the sugars fully dissolve and the mixture begins to gently simmer.
Add the mashed banana and cinnamon. Simmer for 5–8 minutes, stirring occasionally.
Remove from heat and stir in the vanilla extract.
Strain the syrup (optional for a smoother texture) and let cool.
Transfer to a jar or bottle and store in the fridge.