This is incorrect, or at least very misleading.
Players are never allowed to use any artificial intelligence tools during a game. You can only analyze the game with AI after it has finished.
Here is the policy from the Terms of Service
No Cheating or Computer Help
You can NEVER use Go programs (Leela, Zen, etc.) or neural networks to analyze current ongoing games unless specifically permitted (e.g., a computer tournament). The only type of computer assistance allowed is games databases for opening lines and joseki databases for corner patterns in correspondence Go. You cannot receive ANY outside assistance on live or blitz Go games.
The “Disable/Enable AI review” option in the menu to the right of the chat box only changes whether or not you can see the AI review that automatically happens after the game is finished.
The original poster does not even seem to be asking about AI analysis, but rather the use of the “Analyze Game” feature (for exploring variations), which (as others have explained) is available as an option to use if the game was created with that enabled. As long as that feature is enabled, you can use it. If it is not enabled, you should not use circumvent it (e.g., by exploring variations on a separate board). Whether or not analysis is enabled can also be found in the game information.