real_aurgathor Bonhoeffer was also a member of German Intelligence Service, the Abwehr. Make of that what you will.
The best biography of Bonhoeffer is “Dietrich Bonhoeffer: A Biography” by Eberhard Bethge. Bethge was Bonhoeffer’s confessor as well as closest adult friend.
A good summary of the biographies of Bonhoeffer can be found here. https://www.lutheranforum.com/blog/a-readers-guide-to-bonhoeffer-biographies
Under NO circumstances accept Eric Metaxas’ “Bonhoeffer: Pastor, Martyr, Prophet, Spy” as definitive. If you do, read the criticism of it. The book is deeply flawed.
“However, as a number of Bonhoeffer scholars have pointed out, Metaxas assumes an “omniscient” view of what Bonhoeffer was thinking at any given point in time, and this strategy is almost always in service of recruiting Bonhoeffer as a warrior on his side of the contemporary culture wars. This, it must be said, is a particularly distasteful exploitation of the atrocities of Nazism. While scholars of Bonhoeffer might be gratified for the increased attention to his legacy brought by Metaxas’s notoriety, the biography itself should be distrusted.” (cf. summary above)
I could say more, but I would be diving deep into Christian theology, and that is banned.