During WW2, Im curious if the US considered the possibility of a neutralized Japan but successful Germany. If so, we're any plans drawn for a post-war relationship with Nazi Germany?
Are you asking if the US had any preparations or backup plan to settle with Germany and normalize some diplomatic relations? I am not aware of any... that sort of thing doesn't take a lot of planning besides identifying what conditions you are willing to settle for... and having that list would be a dangerous for politics both internal and external to the US. The other Allies were paranoid that the US would settle after neutralizing Japan, which led to the "Germany First" plan.
There were several color prewar plans, notably the RAINBOW plans which had the US with various allies (or none). In those, often the US sought to stablize the European or Atlantic first before moving to advance in the Pacific.