How to call a function every x frames?

Hi,

OnTriggerEnter2D runs once when the object enters a trigger collider. So your if statement only runs once.

You can use OnTriggerStay2D which will run every physics frame (50 fps).

 private int interval = 11;
 
 void OnTriggerStay2D(Collider2D col)
      {
          if (col.gameObject.tag == "BoucleUneEtMelodieUne" && Time.frameCount % interval == 0)
          {
                  PlayBoucleUneEtMelodieUne();
          }
      }

Or you can use a boolean to check if you're inside the trigger or not. Then you'd use OnTriggerEnter2D and OnTriggerExit2D to flip the boolean, and in your Update() or FixedUpdate() you'll be running the if statement along with the boolean:

 private int interval = 11;
 private bool insideTrigger = false;
 
 void OnTriggerEnter2D(Collider2D col)
 {
        insideTrigger = true;
 }
 void OnTriggerExit2D(Collider2D col)
 {
        insideTrigger = false;
 }
 
 void FixedUpdate () 
 {
        if (col.gameObject.tag == "BoucleUneEtMelodieUne" && 
           Time.frameCount % interval == 0 && insideTrigger)
          {
                  PlayBoucleUneEtMelodieUne();
          }
 
 }

I'd suggest trying the former first.