Download file is missing, looking for some texture and materials, unity environment package is outdated and missing.
The standard assets that were originally included with Unity has been removed in latest versions of Unity. You can still download it as a separate package here: https://assetstore.unity.com/packages/essentials/asset-packs/standard-assets-32351
It contains the environment textures used for leaves/water/grass/etc. Personally I would use some more updated textures from something like GameTextures: https://beta.gametextures.com/shop?order=popular&tags=Leaves