BlueStacks Keyboard & Mouse Not Working – Keymapping Fix

Keyboard keys don't register in BlueStacks, the mouse doesn't click in the right places, or keymapping doesn't work in games like CODM, Free Fire, or PUBG Mobile. Sometimes the keyboard types normally in the BlueStacks search bar but does nothing inside a game — or BlueStacks shows the keymapping overlay but inputs have no effect in-game. How do I fix keyboard and mouse input in BlueStacks?