According to the search results, iron can be found at all levels in Minecraft 1.20, from Y-level -63 to Y-level 320. However, it is most commonly found between Y-level 15 and Y-level 232. The best level to find iron blocks is between Y-level 15 and Y-level 232, and the closer you are to Y-level 15, the more likely you are to discover iron. Iron can also be found in iron ore veins, which can generate between Y-level -8 and -56. It is important to note that there is a small gap from Y-level 73 to Y-level 79 where no iron ores are generated. Therefore, the best Y-level for iron in Minecraft 1.20 is between Y-level 15 and Y-level 232.