The light reflects with the ground depend on the direction

[FoxysFox]

I have the default light of UE5 and depending on the direction you are looking at is like the ground and the grass reflects the light.

No reflecting:

Reflecting:

Ground mat:

Grass mat:

In both materials I have all the settings below translucency are default.

[BananableOffense]

This is because the grounds surface normal is pointing towards the sky, but the grass blades normals are pointing perpendicularly to the sky. This means that one side of the blade of grass will be lit, while the other will be shaded.
This is technically correct, but does not look natural.
There are a few ways to address this. One of the most common is to alter the grass mesh normals in either the model or the material to point parallel with the blade of grass instead of perpendicular to it.
You can also enable the “two sided foliage” shading model, which will allow light to transmit through the blade of grass, and preventing it from being so heavily shaded.

[FoxysFox]

How I change it to point parallel to the blade if its a curve?

This is how are pointing now

[BananableOffense]

Vertical is fine too. But you need to be sure that both the front and back face are pointing up.

[FoxysFox]

Thanks a lot it worked