Are modern United States Coins Collectibles?

Could you elaborate on the notion of modern United States coins as collectibles? Are there specific criteria that determine whether a coin is considered collectible, such as its age, rarity, condition, or design? Additionally, how do these factors influence the value and demand for modern US coins in the collector's market? Is there a growing trend among collectors to invest in more contemporary pieces, or do they primarily focus on older, historic coins?