Hello, Ayush! According to Webster's Dictionary, "many a" is used with a singular noun to refer to a large number of things or . In this case, they are essentially saying the same thing in both sentences. "Many a" is not commonly used and is seen more in writing than in spoken English. I hope this answer suffices. Please let me know if you have any more questions! Also, if you're interested in taking conversational English lessons with a teacher, I'm currently accepting new students! https://teach.italki.com/teacher/5129645

Jazz gives a great answer here. I would add that 'many a' is an idiom. It is important to distinguish idioms from the regular meaning of words, as even native speakers who are unfamiliar with the idiom may have trouble deducing what it means. There is a dictionary which has a section on idioms. In this case, it correctly points out that this idiom is always followed by a singular noun. In my experience, this idiom is used for style when narrating a story.