Is it possible to translate this sentence as: You are learning about him? DL marked me wrong, yet in other examples "von" is translated as "about".
With prepositions, it always depends on the context, because they rarely translate 1:1.
In the context of learning, you would learn von someone, but aus a book. It's kind of like "from" compared to "out of".
how would we say "You are learning of him" (as in about him, about a person)
in german you would commonly add "something"
"Du lernst (etwas) über ihn."
Ihm is the dative case form of "er". The "von" in this sentence makes "ihm" the indirect object and changes it to dative case.
von ihm is not an indirect object or any kind of object.
But ihm is dative because von requires the dative case.
they mean the same thing