How can you know if Joseph Smith was a true prophet? Prophets since Joseph that are part of the Mormon church say we can know by reading the Book of Mormon and praying about it. If the Book of Mormon is true then Joseph was a prophet, which means Brigham Young was a prophet and Nelson is the prophet. There are some problems with this. The church split into multiple branches after Joseph died. In the brighamite branch we believe the myth that Brigham Young transfigured into Joseph which indicated Brigham Young was the leader of the true branch (see this https://reasoningmywaythroughmyfaith.blogspot.com/2021/06/god-cant-see-future.html for info on that particular myth) so if we ignore the transfiguration which likely didn't happen then gaining a testimony of the Book of Mormon only tells you that Joseph was the prophet, you have no assurance that Nelson is the correct successor to Joseph. So, what are we to do? Supposedly God gives us evidence which is why we have the Book of Mormon but what about current prophets? If we turn to the bible God gives us another tool to use to determine whether or not someone is a prophet. In Deut 18:22 says that if a prophet speaks in the name of god but the thing doesn't happen, then that person isn't a prophet. There is no JST for these verses, so we can assume God didn't want to change that verse when Joseph rewrote it. So if we can find things a prophet said while speaking for god that didn't happen, then we know they aren't prophets. Joseph said people who were children in the 1840's would see the second coming https://archive.org/details/historyofchurcho05robe/page/336/mode/2up D&C 84:5 says that the current generation (as of 1832) wouldn't die before a temple was built in Independence Missouri. There is still no temple in Independence. That's just two examples and based on the criteria in the bible Joseph was not a prophet. Since Joseph most prophets have been too afraid to make actual prophesies (https://www.fairlatterdaysaints.org/answers/Mormonism_and_science/Joseph_Fielding_Smith_claimed_that_man_would_never_walk_on_the_Moon conveniently fair can claim these were opinion, but he was talking at a stake conference in the second example, if we can't trust that the presiding authority is speaking for god when he speaks at a stake conference then why should we bother going?). Nelson said that 2020 general conference (https://www.churchofjesuschrist.org/study/general-conference/2019/10/57nelson?lang=eng) would be memorable because it would be all about the restoration. It wasn't memorable, it fell flat because people were way to concerned about the pandemic to care that the church had a new special proclamation about the first vision or a new logo. That might be a stretch, you can decide. But if Joseph wasn't a prophet then how could Russell Nelson be a prophet? And as a prophet how is it fair to us for the prophet to say "I was just speaking as a man" or "that past prophet was just speaking as a man" when something doesn't work out. Wouldn't a God of order either, give us a clear straightforward way of knowing when the prophet was talking as a man versus the mouthpiece of God or wouldn't he make the prophet clarify when he was speaking for God versus sharing his opinion? That's a bit of a cop out to claim someone was speaking as a man years after he said something stupid.
This raises another question, why have prophets become less willing to prophesy and instead they simply make generic promises like feeling the spirit stronger or something? Is it because they know it's too easy to be proven wrong? Or does God not have anything he wants us to know about? Throughout the book of Mormon and bible there were plenty of prophecies from every prophet that came true (according to the scripture) Why don't our prophets prophesy? Google a list of natural disasters over the past 100 years. There are numerous events where thousands or even hundreds of thousands of lives could have been saved with a prophecy and some preaching (which happened all the time in the scriptures). No one has done that though. In fact in 1918 the current Mormon prophet died from the spanish flu pandemic, that's pretty unprophetic to die from something you would have foreseen if you lived in bible times. It seems like maybe prophets don't currently walk the earth, and with god's promise to be the same forever it makes me think he never had any prophets to begin with, the bible and churches are all just a big con. I find it much more likely that God created us and is totally hands off letting us gain experience, than I do that he would call so many prophets in bible times and have them perform miracles, prophesy the future and preach the gospel but then change completely so that current prophets look more like business men running a large corporation.