I've noticed when listening to some recordings of ん before a vowel, such as 万{まん}円{えん}
, that the ん sound tends to be assimulated and almost vanish into the vowel's sound (sounding almost like まーえん). But there's just a hint of a naselization I think is being said, but I can't seem to replicate it at all, and pronouncing it with a ŋ ('ng') sounds stronger than the recording.
I've searched some of the past questions on the site related to how ん is pronounced prior to a vowel, but I haven't found a response that really gives a precise answer, as most say 'nasalized vowel' without many instructions on how to actually pronounced it.