By default FlatRedBall projects link pre-built binary files including prebuilt FNA libraries. You may want to link your FlatRedBall project to FNA source for improved debuggability or to contribute back to FNA.
This document includes the required steps for linking your game to FNA.
Linking Your Game to FRB Source
Before you link your game to FNA, you must first link your game to FRB source. If you do not do this, then the FlatRedBall.FNA nuget package will include FNA which results in the FNA libraries being included twice.