On the other hand, if a male turtle is slapping a female, it’s likely a way of showing affection. Finally, if the two turtles are very young, hitting each other is probably just a playful action. Jal Jeev continues by saying that the slapping is typically seen in smaller breeds of turtles, although it’s not clear what kind of turtles these are.

Source: https://www.distractify.com/p/why-do-turtles-slap-each-other-in-the-face