Some of the meshes use double shader(included) for display two-sided polygons. HDRP & URP double sided shaders are better.
There are HDRP & URP renders inside the packages, please read help file inside 'Shaders' folders, use my email if you have some questions.
The links to the assets' pages from the pack:
Eater2
https://assetstore.unity.com/packages/slug/301015
Monsterr3
https://assetstore.unity.com/packages/slug/288463
Worm2
https://assetstore.unity.com/packages/slug/2847271
Worm3
https://assetstore.unity.com/packages/slug/297668