I’m trying to create a regular landscape, and I have a strange display of foliage and trees on it, please tell me what could be the problem?
Looks like you are using a fairly standard shadowing technique to fake clouds.
This is usually within the grass material.
You will probably see a WPO positioned texture that is set to offset or override either normals or base colors.
Usually, you run the same texture with the same parameters over the landscape, and the trees, and you get some cheap, fake, but rather convincing cloud cover.