Is alone noun

No, the Word 'alone' is an adjective and an adverb.

• An adjective is a Word used to describe a noun.
• An adverb is a Word used to modify a verb, an adjective, or another adverb.

A noun is a Word for a person, a place, or a thing.

Examples:

My savings alone won't cover these expenses. (adjective)

She sang alone before a huge audience. (adverb)

Note: The nouns in the examples are savings, expenses, audience; Words for things.