For most artificial sweeteners or sugar substitutes, there are very few or zero calories. You can use them in your drinks during fasting and they will not break your fast.
However, limit the amount you use, as too much of these may cause discomfort to your stomach or even diarrhea. And a study has shown that artificial sweeteners can increase the risk of developing glucose intolerance and metabolic syndrome.
Artificial sweeteners such as Stevia, Swerve, Aspartame, Monk fruit, Erythritol, Allulose, and Splenda won’t break your fast.