WhatsApp does not have a true temporary deactivate option
Turn off notifications in your phone settings
Force stop WhatsApp on Android
Disable background app refresh on iPhone
Turn off mobile data and Wi-Fi for WhatsApp
Log out by removing the app from your device
Back up your chats before uninstalling
Uninstall WhatsApp temporarily
Reinstall WhatsApp later to reactivate it
If needed, delete your account from WhatsApp settings for a permanent deactivation