Should these be these?

[MQi.1]

I found these prompt in my "main.c" of NonSecure generated by MX for NUCLEO L552ZE-Q:

 /* USER CODE BEGIN WHILE */
 while (1)
 {
 /* USER CODE END WHILE */
 
 /* USER CODE BEGIN 3 */
 }
 /* USER CODE END 3 */
}

should it be this?

 /* USER CODE BEGIN WHILE */
 while (1)
 {
/* USER CODE BEGIN 3 */
 
 /* USER CODE END 3 */
 }
 /* USER CODE END WHILE */
}

[KnarfB]

No. These are 2 user code blocks around the beginning and ending of the loop. Some additional software packs may generate code inbetween those (near line 5), do not use it for user code.

[MQi.1]

So, if one need insert code behind while(), where should it be pasted?

[KnarfB]

You can add user code by inserting new lines between 1 and 2 (before while), 3 and 4 (inside while), 6 and 7 (inside while), or 7 and 8 (after while) as you like.

Code behind while(1) {...} is unreachable however.

[Piranha]

Except, if break is used. Or even goto... :)