Years ago I saw a news report on 60 Minutes (I believe) in which the US Army has thousands of art items from the Nazi Era in storage. Kept in perfect shape they are to be returned to Germany long after the stench of nazism is past.
“Art from the Nazi era” is not necessarily Nazi art. The Germans in that time made some spectacular statues and objects of art that on their own did not have anything to do with the NSDAP.
Even if it was Nazi art, so long as he kept it to himself then what was the harm?
The way things are going these days, that’ll be on the 32nd of Notever.