In English, I'm used to saying "in the morning," which "maps" into "Im Morgen." I don't say "on the Morning," which might translate to "am Morgen."
Z.B., I have always said, "Im Morgen gehe ich in die Arbeit." (In the morning I go to work.) I wouldn't use "Am Morgen" in this context. (Maybe someone else would.)
But in this hit song Conny (Cornelia) Froboess, a native speaker sings:
Mein Herz schlägt dabadabada
Am Morgen dabadabada
Am Abend dabadabada
Ein ganzes Leben...
That suggests that "Am Morgen" is correct in German. So would a German speaker also use "im Morgen" in this context? Or is it true, as an answerer said, "Am Morgen" is natural German, and "Im Morgen is not." Have I been using "im Morgen" wrongly up to now?
And the second verse goes:
Mein Herz schlägt dabadabada
In Liebe dabadabada
In Sorgen dabadabada
Ein Tausend Schmerzen Voll Seligkeit.
Here, the preposition "in" is used. Is that because "Liebe and "Sorgen" are abstract nouns, while "Morgen" and "Abend" are "time" nouns.
[There's a last line in the first verse I can't make out. It sounds like "Vor Freitheit und Leicht" but that doesn't make sense. Bonus for transcribing this line.]