Harith (حارث) is a valid name. Its meaning is: "one who cultivates the land; one who strives and works hard."
Sunan Abi Dawud records the following: Abu Wahb al-Jushami, who had the honor of being a Companion, reported that the Messenger of Allah ﷺ said: "Give names after the names of the Prophets. The most beloved names to Allah are Abdullah and Abd al-Rahman. The most truthful names are Harith and Hammam, and the most disliked and ugly names are Harb and Murrah." (Hadith: 4950, Kitab al-Adab, Bab fi Taghyir al-Asma')
Allama al-Khattabi explains that Harith and Hammam were called the most truthful names because Harith means one who strives and works hard, and Hammam means one who has firm resolve and determination. Since every person is engaged, with their resolve and effort, in striving either for this world or for the Hereafter, both names carry complete truthfulness in their meaning.
The Quranic verse: مَنْ كَانَ يُرِيدُ حَرْثَ الْآخِرَةِ نَزِدْ لَهُ فِي حَرْثِهِ also points to this reality, showing that every person, in essence, is a harith, that is, one who toils and seeks to earn.
Allah the Almighty knows best.
Darul Ifta Al-Ikhlas, Karachi.