أحسن الله إليكم I don't understand the term المئنة والمظنة and when it comes to the application to certain rulings like sleep braking wudu. When do we apply المئنة in this situation but not when we get other doubts like. "Did I break my wudu or not? I dont remember"

And when it comes to sleeping, it breaks the wudhu. It's as simple as that. Don't overcomplicate things for yourself. The exception, of course, is if you sleep a very light sleep while you are sitting; for example, if you just dozed off. It was reported by the companions that they did so and stood up and prayed right afterwards. When you have this kind of very light sleep that happens for a very short time while you are sitting and waiting for the salah, this is not a problem, inshallah.