In the following sentence, should Americana be capitalized?
Here's a list of great Americana books.
It looks so weird when written lowercase.
Adjectives that derive from a proper noun are written in capital case; it is also true for nouns, even if in some cases nouns that derive from proper nouns are not written in capital case.
To notice that the adjectives I reported in the list are also used as nouns.
Yes, similar to national adjectives, Americana should be capitalized. Here's a reference