Where to set it up: Settings → Privacy → Privacy lock. Set a 4-digit PIN and you're ready.
Lock in one click: choose "Lock now" in the avatar menu or the canvas menu (top left), or press ⌘⇧L (Windows: Ctrl+Shift+L). The whole page is covered right away, and the browser tab title changes to "Locked".
Unlock: tap the on-screen digits or type your PIN on the keyboard. After 5 wrong tries in a row, wait 30 seconds.
Refreshing won't unlock it: every XinYu tab open in the same browser locks and unlocks together.
Auto-lock when idle: optionally lock after 1, 5 or 15 minutes without activity.
Locking only covers the screen. Generations already running keep going.
Your PIN stays in this browser on this device and is never uploaded. You'll need to set it again after signing out.

New privacy lock: cover your screen in one click, unlock with a 4-digit PIN