Flask: call loop AJAX post when click on a button

In my Flask App, when i click on the "Play" button, I want to display in the DOM some information processed by the server every 4 seconds for 'n' times. With "sync" AJAX POST it works, but isn't the best practice (freeze UI). Is there a better way to do that ? Thanks in Advance

Here is an Example

Flask.py

@app.route("/play", methods=['GET', 'POST'])
def play():
    time.sleep(4)
    # Do something
    data_to_client = {}
    return json.dumps(data_to_client)

Ajax POST

var i=0;
do{
 i+=1;
 $.ajax({
  type: "POST",
  url: "/play",
  contentType: "application/json",
  async: false, // method to change 
  data: JSON.stringify(data_to_server),
  success: function(data_from_server){
   // Every loop changes something in the DOM
  }
 });
}
while(i<=5)

HTML

<div class="col-md-auto p-3 border-top border-bottom">
   <input type="submit" id="play" name="play" class="btn btn-success float-end" value="Play">
</div>

source https://stackoverflow.com/questions/70832981/flask-call-loop-ajax-post-when-click-on-a-button