You are correct that it’s a normal map issue. This one may be a little more difficult to solve since the grass has no base and its normals are so contrasting with the ground.
However, a method that might help is factoring in your RVT normals. Assuming you’re using a lerp for the blending, you can also lerp the normals between your grass normals and your RVT. This tutorial goes into the process of converting them to the correct spaces and combining them. Here’s another great written tutorial that covers a very similar process.
As @doctorpepperdan mentioned, using the material PDO dithering can also help, though this can really start to mess with shadowing so you can’t push it too far.
Likely, a mixture of these two methods will look the best for you. Good luck!