That could be a variety of things.

Start by replacing the post cat 02 and seeing if that clears the code (btw, that is an emissions control 02, not an engine fueling 02). Because you are only getting a post cat code, it seems the fueling sensors are working properly.

The evap system not working is probably related to this, because that recylces fuel vapors and perhaps injects them downstream for combustion later. I cannot remember how the evap system works in theses cars.

Anyhow, I would start by replacing the 02 it says is faulty and seeing if that clears at least the 02 sensor code. It could be indicating cat failure, or something further upstream related to fueling, since lean means not enough fuel is getting to that side, or it is just burning too hot.

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2001 E53 3.0 5pd