Is almost a noun

No, the Word 'almost' is an adverb, a Word that modifies a verb, an adjective, or another adverb.

Examples:

We almost missed the exit. (the adverb 'almost' modifies the verb 'missed')

I touched the almost dry paint to test it. (the adverb 'almost' modifies the adjective 'dry')

We almost always go to a beach on vacation. (the adverb 'almost' modifies the adverb 'always')

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