Thank you for your reply
I have one more question.
The data sheet says that if It don't use an external crystal as shown below, use a ring oscillator.
"If no external crystal is present, then the ring oscillator is utilized"
As you said, if I set up RTC_XTALI, XTALO PIN, could it crash with the RTC module (36.768Khz) due to ring oscillator operation, causing boot problems or other problems? Or would it have no impact at all?