“That’ll Do” Can Mean “That’s Enough” or “That’s Fine”

In everyday Australian English, “That’ll do” often means “That is enough” or “That is acceptable”. If someone is pouring milk and you say, “That’ll do, thanks”, the tone is usually friendly: you have enough.

Spoken alone with strong emphasis, however, “That’ll do!” can tell someone to stop behaving badly—closer to “That’s enough; stop now”. It is not automatic praise. “It’ll do” may also be a lukewarm judgement meaning something is merely adequate. Listen to tone and context; adding “thanks” is the safer way to signal polite satisfaction.

https://dictionary.cambridge.org/dictionary/english/that-will-do