According to the search results, the Y level for diamonds in Minecraft 1.20 is below layer 16, and they can be found between Y levels -64 and 16. The best level to mine for diamonds in Minecraft 1.20 is Y-level -58 or -59. While the best level to find the most diamonds is technically Y-level -59, it is recommended to mine for Minecraft diamonds at Y-level -53 because the lava level is at -54, and underground lava lakes will form at -54 specifically. Therefore, the best way to stay safe and find diamonds is to stay one block above it.