The four letters ي، ن، م، و are gathered in «يَنْمُو». When one of them begins the next word after still nun or tanwin, the nun is joined to it through assimilation with ghunnah. The independent n stop is not pronounced, but measured nasal resonance remains.
«مَنْ يَعْمَلْ» — ya: assimilation with ghunnah.
«مِنْ نِعْمَةٍ» — nun: nasal assimilation.
«مِنْ مَالٍ» — mim: nasal assimilation.
«مِنْ وَلِيٍّ» — waw: nasal assimilation.
One cannot simultaneously pronounce a completely separate clear nun and assimilate it fully. The next consonant becomes prominent while the required nasal quality remains.