Finally I found out why we say “Ghufranaka” when coming out of the bathroom
We say “Ghufranaka” (I ask for Your forgiveness) after leaving the bathroom because it is reported that the Prophet ﷺ would say it.
The meaning behind it is simple but meaningful:
You spend a short time in a place where remembrance of Allah is naturally reduced, so when you come out, you return by asking forgiveness. It’s a way of acknowledging human weakness and asking for a “reset” after a moment of necessary but worldly activity.