Hello, author. How can I eliminate these strange shadows cast by non-light sources (sunlight, moonlight)? I tried turning off ambient light to remove them, but doing so makes the scene too dark. Could you please tell me how to get rid of them? Thank you.

If you disable shaders you will see the same sort of shadow. This is the normal Minecraft lightmaps at play. It's because there are either blocks above those spots blocking the light, or a lighting engine error, just place a block there or something if thats the case.

You cannot remove them, unless you hide it by making minimum light extremely bright.