During the 1930s during the time the Nazis took power there were Nazi flags covering the alters of the churches in Germany as Bohnhoeffer reported and rejected. Stop kidding yourself.
The pastors who covered their alters with the Nazi flag were Lutheran, by the by, as you can find out with a bare minimum of research.
The so-called Roman salute is practiced in Catholic Churches today, in America as well as in Germany and all over the world. I gave that salute many times myself, most recently, in all likelihood, last Easter, and look forward giving it again.
That the Nazis injected a patriotic or even partisan meaning into it does not mean everyone exchanging it was a Nazi, or could predict that it would have a sinister associations a decade later.
Everybody knows how much worse the killing would have been if the Church supported Nazism; I’m sure most Catholics of the time knew how much worse Communism was (The examples of Spain and Ukraine were there for all to see), and simply watched 2 devils fight it out hoping to come through it alive.
Also, when von Stauffenberg sought permission from his Bishop to assassinate Hitler it was a Catholic he spoke with, Cardinal Peysing, not a protestant.