How can I increase Shadow Distance without decreasing quality?

I have a project for an open world game, so I created a terrain and created a Directional Light to test the environment with no objects, only the terrain, I increased the Shadow Distance property in the quality settings to see the shadows from the mountains that were far from the camera, everything seemed good

But now that I added an object I see that the shadows casted from the cube looks very bad

I have read that the problem is the resolution for the directional light, it seems to be static and not dynamic according to the shadow distance, I tried fixing the problem by adjusting the shadows cascades but they doesn't seem to fix the problem because I have to reduce the first cascade size (From a setup of 4 cascades) to the minimum but when I move the camera some units away from the object, the shadows from the object change to the next cascade

What can I do to fix the shadows?

Is there something that I'm missing?