As I said in a comment under Nobody's answer I think the figurative use of Fingerübung is idiomatic and expressive, even though the Duden entry (b) is not describing it (but a piece of music written or played for the purpose of exercise, an étude).

It turns out that there is an exact English equivalent, the five-finger exercise, which can be used figuratively as well.

Other suggested translations like child's play or easy-peasy miss the learning or preparatory aspect which is usually present when Fingerübung is used. At least child's play has an exact counter-piece in German which would be used to express exactly that.

As I said in a comment under Nobody's answer I think the figurative use of Fingerübung is idiomatic and expressive, even though the Duden entry (b) is not describing it (but a piece of music written or played for the purpose of exercise, an étude).

It turns out that there is an exact English equivalent, the five-finger exercise, which can be used figuratively as well.

Other suggested translations like child's play or easy-peasy miss the learning or preparatory aspect which is usually present when Fingerübung is used. And if one wanted to express child's play one could use the exact German counter-piece Kinderspiel instead of Fingerübung.