Prophet muhammad saw is the last prophet sent by Allah so that means all other people who preach after his death are fraud and all other religions that came after his death are also fraud?
Yes. Absolutely based on below evidence.
It is He Who has sent His Messenger (ﷺ) with guidance and the religion of truth (Islam), to make it superior over all religions even though the Mushrikun (polytheists, pagans, idolaters, disbelievers in the Oneness of Allah) hate (it). Quran (9:33)
And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers. Quran (3:85)