: Spamming F3 and A in Java Edition reloads chunks, which can briefly allow you to see through walls and locate caves or ores.
: If you are drowning, using an empty bucket on a water block will briefly create an air pocket, resetting your breath meter. 150 Minecraft Secrets You've Never Seen Before:...
: If you hold right-click to block with a shield while entering a portal, the blocking effect can become permanent in the next dimension, allowing you to sprint and attack while still protected. Invisible Walls & Secret Entrances : : Spamming F3 and A in Java Edition
: You can listen for specific ambient cave sounds; if you hear "spooky" noises repeatedly in one spot, a dungeon or ancient city is likely nearby. Invisible Walls & Secret Entrances : : You
: Placing a hay bale under a campfire increases the height of its smoke signal to 25 blocks, making it a perfect beacon for finding your way home.
For more deep-dives into obscure game data, you can check the Secrets of Minecraft series on the official wiki. 297 Minecraft Secrets Mojang Hid From Everyone
: Placing a Guardian in the back of a boat allows it to shoot lasers at other players, effectively turning your boat into a mobile weapon.