Minecraft wiki entry for Altitude, associated text: The highest possible altitude the player can legitimately climb to is Y = 320, although explosions, elytra launchers, piston slime block bounces, and Riptide tridents can all propel the player far beyond this limit.
In Java Edition, mushrooms can appear on the Nether's bedrock ceiling.[6]
Block generation and player construction below and above the build limits can be achieved only through modifying the dimension properties, or mods, such as the Cubic Chunks mod.
The reasoning behind Custom worlds having height limits of ±2032 rather than ±2048 (a binary number notated as 211) is because the lighting system still applies 16 blocks above and below the world, but the Y-coordinates of blocks (which are also used in the lighting calculation) are stored internally using only 12 bits. Therefore, having limits of ±2048 would prevent the lighting system from functioning correctly.[7][8]