Question Terrain trees turn blue and 2D on distance

It's my first time using Unity and I'm making a cartoon environment for my graduation project but I'm a little worried because the trees turn 2d and blue on distance. I need to render the final result in less than a week but I can't work this out. Also, grass and small plants disappear on distance. What is the problem? When I drag the trees directly to the environment they look normal and don't disappear, but it's a big scene and it would take a lot of time, and also it doesn't work for the grass, mushrooms, and flowers. Any help is appreciated! Thanks in advance.

 

@lauraromanc
Under the Scene tab, click on mip map and change it to shaded. Hopefully this works.