In your layout `app/code/Amin/HelloWorld/view/frontend/layout/helloworld_index_index.xml`, `Amin\HelloWorld\Block\HelloWorld` changes to `Amin\HelloWorld\Block\Helloworld` (`Helloworld` has all lower-case letters). And try to rename the view folder `app/code/Amin/HelloWorld/view` to lower case also.

Remember that Magento loads the name of classes with case sensitivity. If we have some troubles when creating a simple module, please check our file structure, naming (including case sensitivity).